In Brady v. United States, 397 U.S. 742 (1970), a defendant, eight years after having pled guilty, attempted to attack the voluntariness of that plea on the ground that it had been coerced because of his fear of the death penalty. The Supreme Court rejected that attack upon the plea. One of these circumstances was the possibility of a heavier sentence following a guilty verdict after a trial. It may be that Brady, faced with a strong case against him and recognizing that his chances for acquittal were slight, preferred to plead guilty and thus limit the penalty to life imprisonment rather than to elect a jury trial which could result in a death penalty. But even if we assume that Brady would not have pleaded guilty except for the death penalty provision of 1201(a), this assumption merely identifies the penalty provision as a "but for" cause of his plea. That the statute caused the plea in this sense does not necessarily prove that the plea was coerced and invalid as an involuntary act. 397 U.S. at 749-50. The Supreme Court made clear that much guesswork is involved in judging the strength of the State's case and in predicting likely punishment. Ill-advised guesses, however, do not invalidate otherwise voluntary and knowing pleas of guilty. Often the decision to plea guilty is heavily influenced by the defendant's appraisal of the prosecution's case against him and by the apparent likelihood of securing leniency should a guilty plea be offered and accepted. Considerations like these frequently present imponderable questions for which there are no certain answers; judgments may be made that in the light of later events seem improvident, although they were perfectly sensible at the time. The rule that a plea must be intelligently made to be valid does not require that a plea be vulnerable to later attack if the defendant did not correctly assess every relevant factor entering into his decision. A defendant is not entitled to withdraw his plea merely because he discovers long after the plea has been accepted that his calculus misapprehended the quality of the State's case or the likely penalties attached to alternative courses of action. 397 U.S. at 756-57.