For a few years I ran a Karaoke band, so every song was an adventure. The surprising thing was how GOOD many of them were. We kept a few phone numbers, and some of them are now regulars on the local bar band circuit. One guy was autistic, and would never have coped with the stress of being in a band, but was a great singer - to him every song was being a real rock star, and he acted like he was playing a stadium! He was at every show, and we knew we could call him up, and he'd do a great job.
The other surprise was how BAD people could be - they'd pick a song, and we had lyrics printed... WHY would you pick a song if you have NO IDEA how it goes? I expected bad singers, but this wasn't just being out of tune - we'd start playing and they'd just start running through the words... no gaps between lines, or verse/chorus, no rhythm... just singing the words one after the other! No regrets though - it was all part of the show: they sucked but they knew it (I hope!) but it was all in fun, and their friends loved it.
More negative experience, different band, had a gig with another band opening. We wouldn't normally do that, but it was a charity event. Of course they over ran, and we ended up finishing our second set at about 1:30, when we were supposed to finish just after 12! Except our singer had used the extra time to get drunk, and decided it would be great to invite the opening band up to play the last song with us. Of course they didn't really know it, but sure... most of the audience left by 1 (no reflection on us honest - just a long night!). We get through it... and the singer wants to keep going and "jam"... I say "NO! we've played our 2 sets, plus encores, and its well over an hour after we should have finished, and its already sounding BAD"... Bass goes in its case, and I'm off to fetch the car. When I get back to load up the guitarist is trying to explain to the drunk singer why he can't just keep going without a bass player, and the bar owner is giving me evil stares (the longer we play the more people drink). 2 days later I get a text (after being in the band 10 years), saying I'm "not a good fit"...
It's all good in the end, as I took 1 month off, and the first band I auditioned for asked me to join - much better pay, more fun music, better people to work with. I avoided the venue for 3 years, but when I went back the owner ran up and gave me a hug, and said how much they missed me!