Tapas is dedication, the sticking to your practice, as described in the Yoga Sutra. It is the first step of Kriya Yoga. It is the third of the niyamas. One of the earliest definitions of the word yoga was discipline. It is tapas, or discipline, that we need now. Once we have learned how to allow the world to be the way it is, once we have learned how to watch all the sensations flowing through our minds, hearts, and bodies, once we have learned to take appropriate action, we need to keep doing this. Over and over again, we build a habit. A habit of allowing, watching, and acting.
Habits are built through repetition; if you can repeat an action every day for twenty-one days, it will become a habit. If you can practice your yoga every day for three weeks, it will be difficult for you to stop doing yoga. If you can practice allowing, watching, and acting for three weeks, it will be difficult to stop allowing, watching, and acting.
Twenty-one days is not a long time.
Each cycle of allowing, watching, and acting takes very little time. Each succeeding cycle will take less effort as well. The more we practice, the easier the practice becomes. But, it does take effort, especially in the beginning. Establishing any new behavioral habit takes effort.