My mind tends to wander quite a bit at all times, so it is easy for me to go down paths of fear and regret. The good thing is, because my mind doesn't stay on any one topic for too long, I usually move on pretty quickly. That doesn't mean the same things don't continuously come back to haunt me over and over again! My biggest fear is probably losing the people I love, but I know my time now with them is precious, so I just try to focus on that.
Yep, it's important to understand that time is limited and when it passes it won't come back; I think that acceptance can help a person live a little better, including the time spent with valued people, in the present.