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.