Well , mistakes are made all the time and sb needs to focus and study the errors , the leaks he has in his game sessions . I always see mistakes in my gameplay on cashgames , unfortunatelly , and always try to analyse them , but I have the bad habit to do this during a session , which sometimes frustrates me (I try to change it and do it at the end or at a different day ) .
But the facto luck is there , when we speak , as sb said , for tournaments (or hyper turbo sng ) , on these tours there's a lot of variance so even if sb makes no mistake , you still have to pass some coinfips and some blind fight etc.
But I agree , the mistakes is the more critical point sb has to correct and pay attention to .