As a child, it's easy to make friends, or at least meet new people. There are natural venues for that. Children meet others in school, in the playground, and in many other venues where children are expected to be in. But as adults, this exercise is harder. Once you're done with school, e.g., university, then there's no more group where its members have a shared set of experiences. Not to mention that there are other distractions, like for example, one's work, or one's children. And so it's harder to meet new people, and make new friends.
In my case, I've been trying to meet new people recently, mostly because I have the impression that the set of people I consider as friends keep on getting smaller and smaller. When I moved to Berlin ten years ago, I made a bunch of new friends, mostly from circles such as Yelp and Couchsurfing. And in the meantime, I found a partner, and eventually I faded away from the Yelp and Couchsurfing communities. Additionally, for most people, Berlin is just a phase. People go to Berlin to try their luck for a few years or so, and then they move on and settle somewhere else. But it seems I am here for the long term, so I need to make efforts to refresh my set of friends and add new people every now and then.
This exercise is not easy. Because it's not dating. For dating, there are dating apps. But for friends, there are apps, but it's a little weird what to expect. So there are alternatives, like joining meetups. I signed up for a Meetup account, but so far I haven't joined any event. We'll see if this goes anywhere.
There's also work. I think I like the people I work with, and therefore I consider a few of them as friends. And yes, colleagues come and go, but there are a few who I still keep in touch, even though we don't work together for the same company anymore.
In the meantime, I keep an open mind. So when a stranger talks to you and strikes a conversation over dinner, you seize the opportunity. This is exactly what happened to me back when I was alone in a restaurant in Barcelona a few weeks ago. I had a table for one, and the next table also had just one diner. We struck a conversation, and I must say, it was a wonderful evening. I don't know whether I'd meet this person again, but at least I had a fun evening.