Cheryl Marie Stagner (Stagner) was convicted of receiving or concealing a stolen Lincoln Continental Mark IY in violation of Wyo.Stat. § 6-3-403(a)(i) (1988).1 She testified that another defendant told her he had purchased the car. She asked the trial judge to give a “Mistake of Fact” instruction to the jury as part of her theory of *521defense. The trial judge refused. We reverse.
Because we reverse the conviction based upon the issue of the refused “Mistake of Fact” defense instruction, we do not address the additional issues advanced by Stagner.
FACTS
The prosecutor presented several witnesses to prove Stagner was guilty of receiving or concealing stolen property. First, a high school teacher testified he had a 1973 Lincoln Continental Mark IV stolen from his locked garage in Huntley, Montana. A Wyoming rancher from Fremont County testified that he had called the Bureau of Indian Affairs (BIA) in the early hours of January 10, 1989 to report two vehicles heading onto his absent neighbor’s ranch.
The two BIA agents testified that they responded to the rancher’s call. They discovered an area that was cluttered with junk vehicles when they arrived at the neighboring property. There they spotted a pickup in pretty good shape that had new Wyoming license plates. One agent approached the pickup on foot and had to peer inside before seeing two people lying down on the seat. He identified Stagner as one of those people. The other agent identified Hal Alcorn (Alcorn) as the other person. One agent testified that a tribal game warden, who had showed up to assist them, spotted a Lincoln Continental Mark IV. The engine was still warm but had no license plates. When they checked the vehicle identification numbers, they discovered that the car had been stolen. When they searched Stagner pursuant to her arrest, they discovered the keys to the Lincoln in her coat pocket. They also found three handguns in the pickup which Stag-ner indicated were hers.
Another prosecution witness, Les Kil-wein (Kilwein), testified that he brought the Lincoln to Fremont County and showed it to Alcorn and Stagner. Although his testimony incriminated himself as well as Stagner, he waived his privilege against self-incrimination apparently on the advice of his defense counsel.
Kilwein testified the stolen car originally had no license plates when he took possession of it in Montana and that he attached a Wyoming license plate to the back. When he got to Morton, Wyoming, he stopped at the Stage Stop Bar. He testified he met Stagner at that bar and told her the Lincoln was stolen. He said she responded by saying they had to get the car off the bar property. Kilwein testified that Stagner drove the car, with him as a passenger, to a field with a trailer house and parked behind the trailer.
Alcorn testified he followed in the pickup as Stagner led him to the ranch around four in the morning. He also testified that when they saw the lights of the BIA agents, Stagner and he tried to figure out a plan of escape and that Stagner was armed.
In attempting to refute this evidence, Stagner testified to quite a different story. Her testimony, relevant to her requested but refused jury instruction, included the claim that Kilwein told her he bought the car in Billings, Montana and had traded a Camaro plus $150 dollars for the car. She further testified that he insisted she take the Lincoln for a drive. She said that when she asked how he could afford the car, he again said he had traded a Camaro plus $150 for it. She also testified that she told the BIA officers that she did not know the car was stolen.
When it came time for the trial judge to give the jury its instructions, the defense attorney asked for a “Mistake of Fact” jury instruction, but the trial judge refused.
The instruction stated:
An act committed or an omission made under a mistake of fact which nullifies the requisite intent as an element of the crime charged is a defense to that crime.
Thus a person is not guilty of a crime if he commits an act or omits to act under an honest and reasonable belief in the existence of certain facts and circumstances which, if true, should make such act or omission lawful.
*522STANDARD OF REVIEW
The standard of review for a requested but refused jury instruction is established by Oien v. State, 797 P.2d 544, 547 (Wyo.1990) and Thom v. State, 792 P.2d 192, 195 (Wyo.1990). “The refusal to allow an instruction requested by the defendant when due process requires the defendant’s instruction be given is reversible error per se.” Oien, 797 P.2d at 549.
In Thom, 792 P.2d at 195, we said “a defendant has the right to have instructions on his theory of the case or his theory of defense presented to the jury if the instructions sufficiently inform the jury of the theory or defense and if competent evidence exists which supports the law expressed in the instructions.” In Oien, 797 P.2d at 549, we said we view the evidence in a light favorable to the accused and that “the accused’s testimony must be taken as entirely true” to determine if the evidence is competent. See Amin v. State, 695 P.2d 1021 (Wyo.1985); Patterson v. State, 682 P.2d 1049 (Wyo.1984); and Reid v. United States, 581 A.2d 359 (D.C.App.1990).
The standard of criminal law that the accused has a right to have a theory of the defense instruction, if fairly supported by the evidence, see 4 Charles E. Torcia, Wharton’s Criminal Procedure § 538 (12th ed. 1976), has a strong and continued history in Wyoming precedent. “[T]he defendant had a right to have his main defense in the case affirmatively presented to the jury.” State v. Hickenbottom, 63 Wyo. 41, 69, 178 P.2d 119, 131 (1947). See Goodman v. State, 573 P.2d 400 (Wyo.1977); Thomas v. State, 562 P.2d 1287 (Wyo. 1977); and Blakely v. State, 474 P.2d 127 (Wyo.1970). See also Best v. State, 736 P.2d 739 (Wyo.1987); Naugher v. State, 685 P.2d 37 (Wyo.1984); Patterson, 682 P.2d 1049; Scheikofsky v. State, 636 P.2d 1107 (Wyo.1981); and Benson v. State, 571 P.2d 595 (Wyo.1977).
DISCUSSION
Whether or not the evidence is competent to support the request for the “Mistake of Fact” jury instruction is critical to our decision. Stagner twice testified that Kilwein told her he bought the car in Billings, Montana and had traded a Camaro plus $150 for it. Under Oien and Thom, such testimony must be taken as entirely true for purposes of testing the competency of evidence needed to support a theory of defense jury instruction. Taking her testimony for the purposes of this review, the evidence is competent to support a “Mistake of Fact” instruction.
Stagner’s testimonial evidence was sufficient to refute Kilwein’s assertion and support the giving of the instruction. It is for no one but the jury to decide who is credible. “The question is whether the defensive evidence raised the issue of mistake of fact, because if it did appellant was entitled to an affirmative submission on the issue.” Lynch v. State, 643 S.W.2d 737, 738 (Tex.Cr.App.1983). See People v. Ellison, 126 Ill.App.3d 985, 81 Ill.Dec. 222, 466 N.E.2d 1024, 1032 (1984) and Willis v. State, 790 S.W.2d 307 (Tex.Cr.App.1990). The refusal to give the instruction under this circumstance violated federal and Wyoming due process. Best, 736 P.2d 739; Blakely, 474 P.2d 127; Stevenson v. United States, 162 U.S. 313, 16 S.Ct. 839, 40 L.Ed. 980 (1896).
The theory of the case instruction, where appropriate evidence exists, is a basic tenet of criminal law and a procedural concomitant of due process. Wyo. Const. art. 1, § 6. The commonly accepted enunciation is “[a] requested instruction on a party’s theory of prosecution or theory of defense must be given if such theory is fairly supported by the evidence.” 4 Charles E. Torcia, Wharton’s Criminal Procedure, supra, § 538 at 11. Initially phrased in Stevenson, 162 U.S. 313, 16 S.Ct. 839, 40 L.Ed. 980 and restated by Chief Justice Rehnquist in Mathews v. United States, 485 U.S. 58, 63, 108 S.Ct. 883, 99 L.Ed.2d 54 (1988):
As a general proposition a defendant is entitled to an instruction as to any recognized defense for which there exists evidence sufficient for a reasonable jury to find in his favor. Stevenson v. United States, 162 U.S. 313[, 16 S.Ct. 839, 40 *523L.Ed. 980] (1896); 4 C. Torda, Wharton’s Criminal Procedure § 538, p. 11 (12th ed. 1976) * * *. A parallel rule has been applied in the context of a lesser included offense instruction * * *.
The Wyoming Supreme Court has generally recognized the due process component of this principle which essentially addresses both the accused’s right to defend and the jury’s right to weigh and assess evidentia-ry validity and sufficiency. Blakely, 474 P.2d 127. Goodman, 573 P.2d at 409 (quoting 23A C.J.S. Criminal Law § 1313) (emphasis added) teaches us that
"the weight and sufficiency of the evidence to establish a fact in issue are a question for the jury, it is generally recognized that any evidence which will authorize the jury to find on it, although in the opinion of the court it may be weak, inconclusive, or unworthy of belief, is sufficient to justify an instruction on the issue raised by such evidence, and even positive testimony is not required, for it is sufficient if the fact in issue reasonably may be inferred from circumstances proved. However, in order to warrant giving an instruction, the evidence should be sufficient fairly to raise the question involved therein.”
The review required by the trial court, Reid, 581 A.2d at 368, directs attention only to the existence of an evidentiary basis for the jury’s consideration and not a criteria of some convincing character of the evidence as analyzed by the trial court or the appellate jurist.2 Oien, 797 P.2d 544; Best, 736 P.2d 739; Dykes v. State, 319 Md. 206, 571 A.2d 1251 (1990); State v. Aubert, 120 N.H. 634, 421 A.2d 124 (1980); Willis, 790 S.W.2d 307; Lynch, 643 S.W.2d 737.
Because Stagner was entitled to the theory of defense instruction she requested, under Oien and Thom, we reverse.
. Wyo.Stat. § 6-3-403(a)(i) provides:
(a) A person who buys, receives, conceals or disposes of property which he knows, believes or has reasonable cause to believe was obtained in violation of law is guilty of:
(i) A felony punishable by imprisonment for not more than ten (10) years, a fine of not more than ten thousand dollars ($10,000.00), or both, if the value of the property is five hundred dollars ($500.00) or more[.]
. What the appellate jurist expects the trial court to do is not the appropriate test to justify denial to that jury of a decisional responsibility. The knowledgeable Fremont County jury in Lander, Wyoming can more responsively weigh believability from the live witnesses’ testimony and demeanor than can the appellate court from a cold record in Cheyenne, Wyoming.