Work life balance
One of the things that is hard to learn and counter-intuitive is managing my own psyche. As the company grows, the complexity of the problem is usually O(n^2), where n is the number of people. The probability of something being broken also increases.
However, you can’t let it affect your psyche. Every interaction/meeting has to be treated in an isolated way. It’s also counter-intuitive because if you’re unhappy with the progress in one meeting, natural human emotion dictates that you’ll be upset going into the next one, but that’ll be catastrophic to the company. You’ve to reset back to zero and look at the next one in an isolated way.