About the worst thing you can do when it comes to working out and dialing in your nutrition is - GUESS. At one end of the spectrum, guessing about how to adjust portions, weights, reps, time and/or rounds costs you efficiency if you get one (or ALL) of them wrong. Being very deliberate about storming your nutrition and workouts helps you to make faster progress. At the other end of the spectrum, anyone who guesses wrongly about any or all of the principles above will likely be subject to some rather harsh penalties, in terms of, injuries and setbacks. Those alone are good enough reasons to keep track of workouts and nutrition.
Wanna know something worse than not making progress, or becoming injured?
It is becoming successful and NOT knowing how you did it.
Think about it. What if you changed 3 things about your diet and/or workouts - AND IT WORKED! Your body, fitness and health jump to a whole new level of success. What do you know? Which thing was it that made the difference? Was it all three? Was it two of the things? Was it just one of them?
The problem is, whatever you are doing now will need to adjusted in the coming weeks, months and years. Your fitness and health won't stand for stagnation. It's the nature of this beast. What you don't want to do is UNDO the thing(s) that is(are) working for you. Which is all fine and good as long as you know what they are. If you don't - you are back to square ONE, man.
Most people would say, It's cool. I'll just keep making changes to ALL THREE of the things. That worked fine the first time.
Seems like a good plan too, but one thing we all come to learn about health and fitness is where one good thing giveth, another good can taketh away.
The only thing your body hates worse than stagnation is inefficiency. Participating in ONE inefficient thing will eventually rob success from all other fruitful pursuits. Truly, one rotten apple does spoil the whole barrel.
It's bad enough not to see much progress when you are putting in real time and effort. It's worse to backtrack and have to start all over.