For me, it was contactless payments. For the longest time I didn't want a contactless card, a little bit out of fear of someone being able to steal just by being close enough but mainly out of "it's such a minor convenience it's not worth asking the bank for the card". Several years go by and the non-contactless card expired, and the new one was contactless, but I still wouldn't use it.

Then one day I did, and holy shit it's the best thing ever, I'm never using cash again (this was before covid hit which has made contactless mandatory now).

I'm sure there are a few other things in my life like this, i.e. things that I'm aware of, but making stupid choices about, I'm just not aware that it's a stupid choice.