The Talmud brings up an ancient scroll called “Megilat Taanit” the scroll of fasts. This was actually a list of quasi holidays on which it was forbidden to fast because of some minor miracle or positive historical event that took place on that day. The Gemara debates if any of these days were still in effect after the destruction of the Temple.
When you accomplish something good, remember it. Make a list of the days on which you realized (or generated) significant growth, even just a personal best in lifting or a sport. Celebrate your own victories. Even “minor” miracles.
When a man focuses on negative events, he not only drags himself down, but he trains his mind to look for problems and losses. He can make himself into an anxious wreck. Be aware of your mental habits, they become your personality.
Fasting in Jewish wisdom is self abrogation and self destruction – you literally eat yourself up. This is sometimes necessary, but not on a regular basis. Celebrate gains or changes you have created by avoiding the “fasting” of indulging in self limiting beliefs or self destructive thoughts and actions.
If you find it hard to identify the positive days in your life, think about what Albert Einstein said: There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
Small miracles are still miracles. Your small victories are still victories.
You can also use such positive days as an opportunity for self care. The Gemara notes that in the city of Lod they once decreed a public fast during Hanukkah, and our sages protested by going to the bathhouse and taking a haircut, and told the people there they needed to fast again to atone for fasting on Hanukkah.

