Would You agree, that most relevant mental characteristic(if all else is equal), is Self-control?

I agree, when I go into a training session with the key point of self control, I always have a good session even if I'm not hitting well at the start. This is an improvement from last year when I got really annoyed when I had bad sessions or matches, usually because of the lack of play limited my ability to fulfill my full potential, Self Control is definitely a Key to success for Some players.

However some player are able to use there anger to their advantage, so you can say it differ between players.

Tennis is like every sport its through the mind not the body , take the 2 matches , Federer V Tsonga at wimbledon this year and Federer V Novak Us open this year , Federer up 2 sets to love in both games lost the last 3 sets to Tsonga and had 2 match points against Novak up 5-3 in the 5th , reason for his loses? cause he was mentally beat in the tsonga game and like last year he had match points on novak and failed to win again , if he would've been 100% switched on he would've won ,