Well, one doesn't wish to be an importunate jackass, either - and avoiding that is a social skill worth having, too. You work your way up from eye contact, to a nonverbal or verbal greeting, possibly to conversation if there's a subject of sufficient interest to all parties - but probably not, unless you both happen to be walking the same way, at the same pace; you're more likely to get into a conversation at a bar or a café than while actually walking. You pay attention to your intuition for people and don't insist on yourself when you get the feeling it isn't welcome. And you don't belabor someone who's clearly not interested in playing along, save in rare exceptional circumstance such as frank physical distress.

I'm a strong introvert in my own right. I assiduously avoided unplanned interaction for years - I still do, often enough, when I've drawn heavily on my reserves and need to recover. But I no longer always avoid them, and I think I'm better off for that. I like to hope that, on balance, the people around whom I tend to turn up are better off for it, too.

(Related: https://news.ycombinator.com/item?id=14889190)

>"Unplanned interactions" is very annoying thing

Most on HN would find the most fulfillment in improving their social muscle, not their calves.

Do you hate unplanned interaction because it is unenjoyable for you? For most people, it's immensely pleasurable.