A topic I've been into lately- outside of health/fitness- has been been personal finance. Learning about things like investing, retirement accounts and savings rates have taken up a lot of time for me lately. I'm not saying I'm on my way to being the next Warren Buffet or anything but I can tell you the difference between a Roth IRA and a traditional IRA. (I think...taxes or something). Anyway, there's an investing principle that has a lot of crossover into health and fitness. The principle states that you can't time the market. Meaning that the best investors don't try to buy/sell stocks based on when the market is up or down. The best investors are in the market for the long term and don't worry about the ups and downs; they know the long term compounding effects of the market is where the real money is made.
This is similar to your fitness routine. We all know those people that go from workout to workout or diet to diet. These people may see some short term benefits from doing this but in the long run they don't see any real changes. However the people that stick to the same workout/diet, whatever it is, see more long term benefits.
The reason people go the former route (workout to workout, diet to diet) is because consistency is hard. Consistency requires you to stay the course when you don't see immediate results or, even worse, when you see negative results in the beginning. This is the equivalent on not selling a stock when it's price drops.
It's hard to watch your account lose money or your weight go up and trust the process. However, this is exactly what you should be doing. Whenever someone asks what's the best fitness routine for them, I always reply "the one you'll stick to."
When it comes to stocks the saying goes "time in the market beats timing the market." The same goes for fitness. Pick a course and stick with it. You need at least six weeks. Give your returns a chance to compound.
(Also for the record I do know the difference between a Roth IRA and a traditional IRA.)