The hardest thing to remember is that nothing I've done or haven't done actually matters to the present moment. In other words, my past actions or inactions do not actually dictate my next action. Not that it’s easy, but it’s certainly possible to untether a present decision from any number of past ones.
This is why regret is so destructive. It tricks the mind into wasting the present moment with rumination on what is past and unchangeable, and, even worse, suggests an inevitability in how an hour, a day, or a year will go, which can never truly be known with any kind of certainty.
If the future is unknowable, and the past is unchangeable, then what is the present?
The only time that matters.
This is not a new concept, it's just hard to hold on to. Gee, I wonder when would be a good time to practice?