It is called chemistry. Some fighters and trainers click and some do not. Rooney was perfect for the 1985-1988 Tyson and I believe he would have kept him in check after that too.
I don't want to be mean, but if you watch interviews with Rooney he's not the brightest guy. Nice guy and everything, but... Wasn't it some other trainer at that point?
Do you know why Cus D'Amato seemed to be grooming Teddy Atlas as Mike Tyson's possible substitute trainer instead of Kevin Rooney? I ask this b/c I remember an early Tyson documentary where Atlas took Mike to amateur fights and worked his corner. I didn't get the picture that Rooney was as involved as Atlas early on. Anyhow, if it weren't for Atlas pulling a gun on Cus's last great hope, which was obviously a sure thing in Tyson but only needed Cus to live longer to see him fulfill his dream of Mike becoming the youngest HW champ--Teddy most likely would've went on to be Tyson's primary trainer. Or is this assessment wrong?
Rooney was still a fighter himself when Mike was in the amateurs; in fact, their pro careers even overlapped a bit. I don't think Atlas was ever intended to be #1 after D'Amato himself. He may have been that just by default in the early-mid 80's just because Rooney was still focused on fighting himself. I don't think Atlas was ever considered his "main" trainer, even in those days.