Many years ago I used to despair every time I used my dad's windows machine. Every time, his browser window was filled with loads of toolbars installed by various sites and utilities, leaving him with a tiny usable content area. I kept explaining why this happened and he never changed his behaviour.
I got him to buy a Mac and for a few years things went well. But then he started complaining about it behaving weirdly or running slowly. I'd take a look and find he'd installed some free utility or some other odd bit of software that was screwing up his machine. I kept explaining why this happened and he never changed his behaviour.
I keep telling him to get an iPad, as at least then everything would be sandboxed and iOS would kill background tasks. But he says, no, he needs a real computer.