About 25 years ago, a friend offered 'Prioritize things that only happen once in life' as an idea for helping me decide whether to go to my friend's wedding or an important work event. The wedding was great, and the idea has been useful in many other situations, none more so that funerals.
That's bad advice to always go to social events. I tried to follow it in order to expand my social circle, but I ended up staying in places that sucked, with people I didn't like. I try to dedicate some effort to tell whether I actually want to attend or not, and then follow through. I follow my gut, but never change my mind after making the decision.
Of course if the only offer you get is places who suck and people you don't like, it's a bummer. Although I don't think the OP meant that - going for going's sake. In a hypothetical situation when the place would be just okay and the people too, some people's brains (mine too) tend to say "meh don't bother, nothing stellar gonna happen anyway". That is the impulse we ought to fight: don't save yourself for exceptional events, but be surprised by the small pleasures in regular ones. And still avoid the bad ones, that goes without saying.
Conversely I went to one high school reunion I was feeling iffy about, had an okay time but was also completely happy just never going to anymore (and haven't).
But there's definitely some other effects in play there: revisiting people from your past who you've lost touch with is a pretty fraught experience, at least for me because ultimately the relationship is at best frozen in time from whenever you last talked: high school is particularly bad IMO, because it tends to feel like just trying not to be who you were a decade ago as everyone remembers you, rather then getting to be who you are now.
I've never been to a high school reunion, and I don't intend to go to any future ones.
But I went to a high school friend's 40th, and caught up with the people who were my good friends - and still are - and it was worth every penny just to hear their voices face to face for a few days.
My 10th reunion was kind of poorly put together and poorly attended. I almost didn't go to my 25th based on that experience.
But it was the complete opposite. There was a committee of four students that planned it, they set up a tour of the building with the new principal in the morning, they rented out a venue that had an almost prom-like feel to it, there was a memorial to four students that had died (three of which I wasn't even aware of, one of which was my friend that shot and killed himself while we were still in high school, so it was nice to see him remembered).
Tons of people were there (like at least 60 people), and I talked to people I barely talked to in high school because I was so shy (and realized my reputation seemed to be a bit higher than I had anticipated, I just thought I was the quiet weird kid), and I was able to remember and reconnect to some friendships I had mostly forgotten about in the years since, and see how these people had changed since up close instead of just some random posts on Facebook.
It was really great for the most part. Only downer was seeing how many people had kids and how old those children were (a few people were nearly empty nesters already), since I still don't have children yet.
9+ times out of 10 when I’m on the fence about going to a major life event and go, I’m glad I did. Can’t think of the last thing I regretted going to.
I’ve certainly missed some like graduations I regret not making it to.
Funerals are towards the top of the list of big life events and I’ve never regretted one.