Letting go of the past.
Seth Godin talks about letting go of sunk costs: things we have invested time, money or energy in the past that do not serve us in the future. This is one of the most difficult skills to build.
If you had to choose from scratch, which habits, people and projects would you take along with you in the future? And what new habits, people, and projects would you look for?
It's a choice between the life you are living right now and the one that you want to live.