We can only do so many things at once. Our effort and attention are finite resources with reserves that can be drained and refilled. To manage this for your health and fitness, you need to know your goal timeframe and the underlying processes your body needs to perform in order to accomplish these goals. This is where informed decision making on the front end of a process can save you significant time and energy.
If you try to work on two things that require opposite stimulus, you will have a very hard time accomplishing both and your effort and attention reserves will drain very fast with little ability to re-fill. Frustration multiplies the pace at which these reserves drain. For example, losing fat and gaining muscle are two things that I rarely recommend going for at the same time, unless you are just starting to lift weights for the first time or can manage the minutia of your life incredibly well. When you want to lose weight, the signal you send to the body is clear. You are asking the body to pull from your stored energy reserves (mostly body fat) because you will not be giving it enough through the foods you eat. You are going to need to be in a calorie deficit and, with that, you can then decide if you want to maximize how much muscle you keep. If you want to maintain your muscle, you need to eat adequate protein and do enough resistance training to send a clear signal to the body. When looking to gain muscle, you are asking the body to build on top of what it already has. You want the body to take the food you eat and turn that into muscle. This requires a calorie surplus, adequate protein, and enough resistance training. One situation requires a calorie deficit and the other a calorie surplus. Tough to do those at the same time. The important takeaway here is that you absolutely need to understand what it takes to accomplish certain goals, otherwise you can choose conflicting things to work towards and potentially accomplish nothing. Look at your effort and attention as valuable and finite resources and it can help you make the most efficient decisions.
-Matt