Poker pundits and theorists state the most common mistake in poker is playing too many hands- by definition, not folding enough (in general or specifically it matters not).
Some time ago I read ( David Sklansky?) folding should be looked at as a smart, profitable play and it has stuck with me ever since.
The problem being a lot of players regard folding as a potential 'loss' of sorts. It isn't. In fact, as we all 'lose' more hands than we win, by definition folding is the profitable play in the majority of hands.
If you have this idea firmly lodged in mind, then making a hero fold becomes a lot easier.