I've always had an easy time talking to strangers and striking up conversations. I think this line is the key one:

> But over time, I came to accept that it’s ok if they didn’t want to talk to me. That’s just one of the things you have to expect when you do something like this.

People are complex! They have a lot going on. You almost never get someone responding with the same attention you are giving. That's just how it is.

What he is doing is developing a practice of friendliness. This won't develop close friendships - close friendships are what happen after you're successfully friendly to people who are good fit. But it will set you up to do well in semi-public spaces like the gym or your friends' party where you don't know anyone. It's an extremely good skill to practice and, unlike what I would have said at twenty, it does not reflect a lack of depth. Understanding that not everyone wants to have a deep conversation at every moment is maturity - doubly so if you can recognize it in yourself.

I have always been good at this and I am pretty introverted. You don't want to force conversations, just start by saying 'What's up?"'. Keep doing it over and over. The is all proved our in social psychology and proximity theory which in a nutshell means you are more likely to get to know people you see more often. You just need to let people know you see them and over time raise the bar.