"I will set sail unless something stops me. I'll become praetor if nothing gets in my way. My business deals will work out unless something goes wrong." This is why we say nothing happens to a wise person that they didn't expect. We don't make them immune to the random events of human life — just to the mistakes. Not everything happens as they wanted, but as they thought it would. Their first thought was always that their plans might hit some obstacle. When you're not completely confident of success, disappointment hurts much less.
I will set sail unless anything happens to prevent me, I shall be praetor, if nothing hinders me, my financial operations will succeed, unless anything goes wrong with them. This is why we say that nothing befals the wise man which he did not expect—we do not make him exempt from the chances of human life, but from its mistakes, nor does everything happen to him as he wished it would, but as he thought it would: now his first thought was that his purpose might meet with some resistance, and the pain of disappointed wishes must affect a man’s mind less severely if he has not been at all events confident of success.