What is a constitutionally deficient performance of an attorney on appeal?

"An attorney's performance is constitutionally deficient if (1) it falls below an objective standard of reasonableness under prevailing professional norms; and (2) there is a reasonable probability that, but for counsel's failings, the result would have been more favorable to the defendant. [Citation.] . . . 'When a claim of ineffective assistance is made on direct appeal, and the record does not show the reason for counsel's challenged actions or omissions, the conviction must be affirmed unless there could be no satisfactory explanation.' [Citations.]" (People v. Grimes (2016) 1 Cal.5th 698, 735.)