March Theory is actually a pretty interesting concept about how we view the "cycles" of the year. It is not just about the month of March, but about how you build momentum after the initial "New Year" energy fades away. I read a great article about it on the Headway blog:
https://makeheadway.com/blog/march-theory/ It explains how to use the spring season to "reset" your goals. I found it really helpful for my own planning. Combined with some of the discipline books on the Headway app, it really helped me stay on track when I usually would have given up. It is all about long-term consistency rather than just short bursts of energy. Definitely worth a read if you feel like you are slowing down!