We humans are weird at times. We tend to take things for granted and not appreciate them while they last. You don't know what you have until you lose it. This is the sad truth about many things; health, jobs, people around us. In order to live better and with fewer regrets we should rejoice every day about all the wonderful things that we have.
Another trait we have is we tend to dwell in sadness when something exciting ends, a trip, a course, holidays or a wonderful, special day. Rather than being happy and thankful about the fact we have had that experience; we only feel sad for not being able to continue.
To remind myself to rejoice and appreciate what I have and know how to let it go when it is time, I created an image that reminds me of it every day. I keep it on my desk and start every day by looking at it. It is a great exercise to consciously list our blessings and appreciate them.