What is the standard for ineffective assistance of counsel?

^4. We apply the following standard in considering defendant's claim of ineffective assistance of counsel: "'To establish entitlement to relief for ineffective assistance of counsel the burden is on the defendant to show (1) trial counsel failed to act in the manner to be expected of reasonably competent attorneys acting as diligent advocates and (2) it is reasonably probable that a more favorable determination would have resulted in the absence of counsel's failings. [Citation.] "[W]here the record shows that counsel's omissions resulted from an informed tactical choice within the range of reasonable competence, the conviction must be affirmed." [Citation.] "In some cases, however, the record on appeal sheds no light on why counsel acted or failed to act in the manner challenged. In such circumstances, unless counsel was asked for an explanation and failed to provide one or unless there simply could be no satisfactory explanation, these cases are affirmed on appeal." [Citation.]'" (People v. Shea (1995) 39 Cal.App.4th 1257, 1265.)