not choosing to socialize may seem like a fine choice and not a source of depression in itself. But I think what the parent tried to say is that there is opportunity cost associated with such a decision. I need good amounts of solitude each week, which makes me an introvert i guess, but if there are no good interactions with other humans at all, my happiness dips noticeably. Having an option to meet with another human (and having a good interaction every so often) is a boost to the feeling of security, which I believe can help the feeling of happiness. For example If i do something awesome (or really dumb), I need to tell someone, and it needs to be someone that actually cares. Or the experience is not as good / might as well not have happened.