1) I imagine outside of non-modifiable factors, the type of practice in which one on chooses to engage has a significant effect on coping. Some may do better with high volume, low emotional contact types of practice (e.g., med management in inpatient). Some may do much better low volume, high emotional contact (e.g., psychoanalysis). Some may do better with children, others adults, others brain injured, etc.
2) avoiding the classic factors associated with psychiatry/psychology boundary violations: lack of social support, substance abuse, etc. Weirdly, being board certified and being a DO is one for you guys.
3) The old old joke: A young, harried, psychiatrist shares a daily elevator ride every day at 6pm with another psychiatrist in his building. The older psychiatrist is tanned, in great shape, well dressed, smiling all the time. After a few years, the younger psychiatrist is burnt out has lost all his hair, put on 30lbs, can't keep a crease in his slacks. In desperation, he asks the older psychiatrist "What's your secret? Listening to other people's problems every day, all day long, for years on end, has made an old man of me.". The older psychiatrist replies, "You actually listen?!"