Sure, I could have instead had a goal of "do as many situps as I can", but for me, that goal resulted in my being able to do fewer situps.

I guess to me it seems automatic to 'unpack' a general goal like that into short-term specific goals. 'Be as fit as I can' became 'Improve my fitness' became 'improve my flexibility and balance' became 'start a martial art and keep doing it until I get my black belt' became a whole bunch of subgoals like 'keep practicing my back kick until I can use it in a sparring match'. It's automatic for me to think about the most specific level of subgoals while I'm actually practising, and only think about the higher-level goals when I'm revising whether to add new subgoals.

I guess, because this is the way my goal structure has always worked, I assume that my highest-level goal is by definition to become as good as X as I can. ('Be the strongest I can' has problems for other reasons, namely its non-specificity, so I'll replace it with something specific, so let's say X=swimming speed.)

I don't know the fastest speed is that my body is capable of, but I certainly want to attain that speed, not 0.5 km/h slower. But when I'm actually in the water training, or in bed at home trying to decide whether to get up and go train, I'm thinking about wanting to take 5 seconds off my 100 freestyle time. Once I've taken that 5 seconds off, I'll want to take another 5 seconds off. Etc.

I think the way I originally interpreted HungryTurtle's comment was that he thought you should moderate your goals to be less ambitious than 'be as good at X as you can' because having a goal that ambitious will cause you to lose. But you can also interpret it to mean that non-specific goals without measurable criteria, and not broken down into subgoals, aren't the most efficient way to improve. Which is very likely true, and I guess it's kind of silly of me to assume that everyone's brain creates an automatic subgoal breakdown like mine does.