Without steadfast awareness our minds will often resort to finding various ways to cause us pain and suffering. One must be proactive in staying a step ahead of our subconscious. Awareness is the key.
Sometimes our mind will focus on regrets from our past, recent or ancient. We will think on regrets we have associated with what we perceive as missed opportunities. We ponder what might have happened if only THIS hadn't occurred, or this other thing HAD. It is important to remember that it is very unlikely that events would have unfolded the way we think they would have if only we didn't miss the opportunity of finding out. This is especially evident as time passes and we tend to have a growing romanticised idea of what might have been. It is completely possible we might have more regret today had we not missed that opportunity and things went sideways. The only truth here is that we will never know what might or might not have been so pondering on it is futile. It is vital to remember this truth and bring it to our awareness the very moment the regrets rear their heads. We might even find ourselves changing from thinking, "Why God did I miss that," to "Thank God that missed me." Don't forget it could have turned out differently than we could imagine with our impossibly ideal circumstances in our imaginations. Just thinking this way for a moment can help ease the pain of regret that we can easily find ourselves completely given over to.
It takes practice to live free of this pain. Meditation can help as well as reading books that deal with these themes. It is also helpful to be part of a group that allows sharing and requires listening to others talk about it.
One day you may listen to someone talk about freedom from the pain of regret and you may see how peaceful and content one can become and you may find that you want that peace for yourself. It can be yours.