Worry and doubt and fear are the major culprits. When you suddenly realize they are there, turn your thoughts to better things. Give those positive things a chance to come to be.
Complaining is another major sidetracker. What do you have to complain about? Aren’t you (weren’t you), even at the lowest point in your life, infinitely better off than so many others? You KNOW you are (were).
And anger… It is a destroyer of whatever you set out to achieve in life, be it relationships, business, sports – there is no upside to anger. Put something else in your mind and heart.
Keep your mind focused on what you want your life to be. That’s the only way to get there.