1. Cracking your Nuckles!
It doesn't causes arthritis. It only causes tissue damage if done excessively. Otherwise, it's completely fine.
2. MSG
It's simply not bad for you! at least no worse for you than standard table salt. The chemical name freaks people out. The headache thing is a nocebo. If people don’t think they’re consuming MSG even when they are, they don’t get a headache.
3. Counting calories to lose weight!
So many people equate it with “starving yourself” or think it’ll automatically result in an eating disorder.
4. Nuclear Power
It's actually very clean and safe, far more than competing power production methods. Even more important is that it's stable, which renewables are not.You need a stable power source to balance renewables, but everyone seems to think burning coal is fine.
5. Being a nice person.
Last but not the least, So many people see being a nice person as showing weakness. That being too nice makes it easier to be taken advantage of, or that it makes you look weak. Despite this, if everyone was a lot nicer a lot more often we would all be much better off.