What is the burden of establishing constitutionally inadequate assistance of counsel?

that counsel's performance fell within the wide range of professional competence and that counsel's actions and inactions can be explained as a matter of sound trial strategy. Defendant thus bears the burden of establishing constitutionally inadequate assistance of counsel. [Citations.] If the record on appeal sheds no light on why counsel acted or failed to act in the manner challenged, an appellate claim of ineffective assistance of counsel must be rejected unless counsel was asked for an explanation and failed to provide one, or there simply could be no satisfactory explanation. [Citation.]' [Citation.]" (People v. Gamache (2010) 48 Cal.4th 347, 391.)