Competent at what specifically? Basic daily life like chores and dishes? External motivators are way better than internal. I never clean "for myself". I clean because my wife needs it for her emotional well-being, and I clean because it would be embarrassing for guest or maintenance to see it.
Other potential options are therapy and medication, but I acknowledge the privelage of having them and that many people dont have that as an option. And obviously I'm just some dude so take it all as anecdotal evidence.
But for me it comes down to I will rarely do things for myself, so mentally framing them as for other people makes it easier
But sometimes "I just couldn't ' is the answer. You dont mad that a fish can't climb a tree. First you ask why the fish needs to be in the tree. And then if it really does, you help the fish get into the tree. Standing behind it shouting words of encouragement or tgreats mean nothing when a fish can't climb. Far too often people get caught up so much on blaming and shaming people for mistakes or failures that it turns relationships sour and the original problem still doesn't get solved.