"If only things had been different..." "What if I had done something else..."

The phrases "what if" and "if only" are often used for regret or to dream of a seemingly better reality...but if you adopt a more fruitful perspective, you can use the phrases to see what you were saved from instead. Regret can be inescapable, but when we wonder "what if" that regret has the potential to turn into something worse. Why does "what if" open the doors to Shaytan, and what are positive ways to use "if only"?