He mentions regularly helping people and then doesn't mention it in the context of how Buffer makes people happy. It's probably assumed, but worth saying: if you're working at a startup, one of the best (maybe the best) feeling is your users telling you how your work is helping them.

It's easy to get caught up in other stuff or forget, but talking to your users/customers and asking them how you're making their lives better is often very revealing and rewarding. It might feel scary/weird to ask, but the answers are awesome.