Let's say someone tells you to stop thinking about that gnome with the red hat. You ask why, what about that gnome and they tell you that it's nothing, it's not worth mentioning. Then of course unwillingly the gnome with its little red hat keeps appearing in your mind.
It is like that with real life stuff, too. You desperately try to avoid a thought and you find yourself thinging about that very thing uninterruptedly. Anyway life still fascinates me and I learned to value the downsides of it, too ^_^.