What negative behavior or trait did you catch in time before It was too late?

Smoking cigarettes. I have been quit long enough that my life expectancy is no different than a non-smoker.
Ideological thinking. There is nothing worse than this. It will destroy you and keep you perpetually unhappy as well as isolate you from others. You will only associate with other people who think like you, and in your narrow echo chamber you will see outsiders as enemies. It’s a sad, sad state for someone to be in. Were it not for different circles I’m in with work, family and friends I easily could have been in only one where ideology dominates. Without exposure to the others I may not have seen it. Far left or right it’s all disgusting and it’s all so very, very wrong.

I changed my career path from music to STEM. Nothing wrong with music but a regular paycheck is pretty nice.

Heterosexuality. It’s a long story, but I married a woman and tried living straight. Thank God I came to my senses before it was too late!

Drinking alcohol. For a few years we had a case each just to start, it started to freak me out since both parents had alcoholism.

Running around all night carousing with buds. My wife pretty much put a stop to that years ago, and I’m glad she did. I’d rather hang out with her anyway. More fun to get out now and then and take a drive in the boonies somewhere, maybe stop at some country diner that we never knew about and grab some lunch. I’ve never missed running with those bums one little bit. So to more precisely answer your Q, in the words of Willie Nelson, “Leaving doubt to fate, staying out too late, waiting for the moon to say goodnight.”