What’s the biggest mistake people make in their 20s?

Gathering bad habits that are hard to break and affect physical health in a bad way. Like smoking, drinking alcohol, gambling, way too much screen time, sedentary lifestyle, taking loans for things they objectively don't need without any real financial security plan how to pay them off...

Stressing over things people say you should do and doing them just because other people say so and not because it's something you truly want and need.