People rise to the expectations you actually hold, not the ones you post about.

Stated expectations are easy and cost nothing; the real ones show in what you assign, who you ask, and what you quietly do yourself because you assume it will not be done well. People read the second set accurately and settle into it. Being told you are capable does not outweigh being treated as though you are not.

Pick someone you have been protecting from difficulty and give them something genuinely demanding. Say you expect it to be good, then stay out of the way. Watch the gap between what you announce and what you hand out.