That in a nutshell has always been his problem; he doesn't know enough capable and trustworthy people. I think he is too trusting and that indicates to me he has a huge heart. Not a bad thing, but obviously he got burned a lot.
I don't buy the argument that all of his former advisors who he now can't stand were bad hires. I think there are two problems, more or less unrelated.
1) He too often hires the wrong people because as a narcissist, he's too susceptible to flattery and therefore hires people not for how good they are at their jobs, but because of how well they can flatter him.
2) When he does hired good people, he has character flaws that destroy the relationship. He doesn't read and won't listen to advice that he doesn't like -- especially when someone tells him he can't do something he wants to do. So he ends up denigrating and insulting those subordinates when they tell him something he doesn't want to hear, and they become "the enemy". In short, it doesn't do any good to hire good advisors if you won't take their advice.
Put those two things together, and they explain why his primary lawyer was a sleazeball like Michael Cohen. Cohen flattered Trump, so he fit 1), and then he wouldn't tell Trump anything he didn't want to hear, even if he had to cut corners or so something unethical, so 2) wasn't a problem.
