Does anyone else, like me, feel to never sell until it is life changing?

In my situation, it makes sense to sell and take advantage of a substantial profit, not life threatening, but enough to buy a nice average car, for example.

Stubborn me refuses to sell because I don't want to know how I would feel if I looked at prices in the future and realized I could have paid off my mortgage. In short, I'd rather lose everything than sell and miss out on mega-profits. It's pretty stupid thinking to be honest.