A player's mental toughness is closely linked to their fitness and the amount of rest and recovery they get - both in the short and long-term.
The Brain Always Wins by John Sullivan and Chris Parker could be quite beneficial to both your coaching and your own personal health and development.
I stopped being what I thought of as mainly a technical coach a number of years ago and began spending more time on the mental side of the game.
We've all had perfectionist players who are really hard on themselves, often without cause. Here are some ideas for dealing with that issue.
Mental training is at least as important as physical training. Are your players at least as mentally fatigued after practices as they are physically tired?