What is the effect of not telling the jury that a defendant must use reasonable means and reasonable force to sustain a claim of self-defense?

We have no doubt that for a claim of self-defense to be sustained, the means employed must have been reasonable. (See People v. Chapman (1946) 76 Cal.App.2d 651, 661 [instruction correctly entitled defendant to "defend himself from apprehended danger to any extent which to him is apparently necessary, acting in a reasonable manner"].) But we cannot see how the failure to tell the jury this could possibly have harmed the defense. On its face, an instruction that the defendant must use reasonable means and reasonable force can only add one more obstacle to the successful proof of self-defense.

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