Under the circumstances of this case, I agree that the trial court abused its discretion in not allowing the defendant to testify at his own trial as a fact witness in support of his defense.
The Texas Rules of Civil Procedure provide that a witness, who is not identified in response to a discovery request, may not testify at trial, unless “the trial court finds that good cause sufficient to require admission exists.” Tex.R.Civ.P. 215(5). This rule helps prevent “trials by ambush.” See Gee v. Liberty Mutual Fire Ins. Co., 765 S.W.2d 394, 396 (Tex.1989). By requiring full disclosure of the issues and facts before trial, the rule permits parties to accurately assess the merits of their case. Id.1 These salutary purposes thus promote the overall objective of the Rules of Civil Procedure, namely, that the rules exist “to obtain a just, fair, equitable and impartial adjudication of the rights of litigants under established principles of substantive law.” Tex.R.Civ.P. 1.
Even a reasonable rule, however, can cause injustice if it is blindly applied without regard to the practical realities posed by the particular circumstances of varying procedural situations. That is why the Court preserved the good cause exception to the general requirement of witness disclosure. Tex.R.Civ.P. 215(5). As we said in Gee, “[sjtrict interpretation of [prior cases] has caused application of the sanction [contained in Rule 215] to be mechanical, leaving no room for discretion. We therefore ... once again point out that the sanction of automatic exclusion of testimony of an undisclosed witness is subject to a good cause exception.” 765 S.W.2d at 396.
Questions regarding the existence of good cause sufficient to allow the testimony of an undisclosed witness belong to the sound discretion of the trial court. See Morrow v. H.E.B., Inc., 714 S.W.2d 297, 298 (Tex.1986). We have drawn the bounds of that discretion so narrowly, however, that in reality, we have almost stripped the trial courts of all discretion in these matters. Before today, there were no opinions issued from this court which held that good cause existed to admit the testimony of an undisclosed witness. See e.g., Alvarado v. Farah Mfg. Co., 830 S.W.2d 911, (Tex.1992) (trial court abused discretion by allowing testimony of undisclosed rebuttal witness); Sharp v. Broadway Nat’l Bank, 784 S.W.2d 669, 672 (Tex. 1990) (trial court abused its discretion by allowing attorney who had not been identified as expert to testify regarding attorneys’ fees, even though attorney had been deposed on that subject and orally identi*93fied as expert);2 Boothe v. Hausler, 766 S.W.2d 788, 789 (Tex.1989) (good cause not established merely because exclusion of testimony would cause “great harm” to offering party); E.F. Hutton & Co., Inc. v. Youngblood, 741 S.W.2d 363, 364 (Tex. 1987) (trial court abused its discretion in allowing an attorney to testify regarding reasonable attorneys’ fees because the attorney had not been designated as an expert). Though Rule 215(5) clearly contemplates potential good cause exceptions to the rule that undisclosed witnesses may not testify, this Court has yet to uphold such an exception. Cf. Alvarado, supra. I agree with the Court that applying the good cause exception sparingly is necessary to prevent Rule 215(5)’s exception from swallowing the rule, and thus undermining the rule’s purpose. However, the rule’s purpose is not served by abandoning all flexibility, rationality, and common sense. As with any equitable exception to a potentially harsh rule, the sensibility of its application depends on the circumstances of the particular case. Rule 215(5) was devised because the Court recognized the potential injustice that could arise from an exception-free application of the rule. If we affirmed the court of appeals’ judgment, that potential injustice would become a reality. Failing to apply the exception simply defeats the plain meaning of Rule 215(5)’s exception.
In TransAmerican Natural Gas Corp. v. Powell, 811 S.W.2d 913, 917 (Tex.1991), we said that “[t]he punishment should fit the crime. A sanction imposed for discovery abuse should be no more severe than necessary to satisfy its legitimate purposes. It follows that courts must consider the availability of less stringent sanctions and whether such lesser sanctions would fully promote compliance.”
We later stated in Alvarado that “[t]he difficulty with [Rule 215.5] lies not so much in the requirement of strict adherence, but in the severity of the sanction it imposes for every breach. The consequences of the rule should not be harsher in any case than the vice the rule seeks to correct. The sole sanction should not be the exclusion of all evidence not properly identified in discovery; rather, as with other failures to comply with discovery, the trial court should have a range of sanctions available to it to enforce the rules without injustice.” 830 S.W.2d 911 at 915 (citing TransAmeri-can) (emphasis added). Having spoken so recently and effectively on Rule 215(5)’s policy, when faced with a clear opportunity to apply that policy, we must do so. To do otherwise would only serve to further exacerbate the increasing ambiguity as to what constitutes good cause. For these reasons, I concur in the Court’s judgment.
. In Gee, we also said that ”[i]f the trial court, in its discretion, finds that good cause exists to allow the evidence, such should be admitted.” 765 S.W.2d at 396.
. I think that Alvarado and Sharp were wrongly decided.