In all honesty, it's riding the emotional rollercoaster of running a company that is often the most turbulent struggle. Sadly, it's seldom discussed (and I'd like to change that).
Founding a startup requires entering a new relationship, perhaps like that between a nurse and a child.
If your company improves, you will leap with joy, and when it suffers you will recoil in rage and sadness. If it dies, your heart will be broken and the level of pain will be hard to imagine. However, all but the deepest wounds recover with time and self-soothing, and you will learn to try again.