Why 173 specifically?
Most people gain weight over time. 2 to 5 pounds a year are not too noticeable until suddenly ya look in the mirror, that's 20 to 50 pounds in only ten years double that for twenty.
It's pretty easy for life to get so distracting that one loses track of their fitness and weight changes.
I know a guy that is exomorphic and weighs less at 50 then he did in high school.
At six feet tall he looks kind of skeletal.
Don't get too fussy about a few pounds, a pint of water is about 1.1 pounds and you can easily change that little amount just by hydrating or peeing.
Intestines also can hold a surprising amount of material & weight.
So I'd say don't worry about actual weight, simply pay attention to how your body looks in the mirror. That's probably what you're really after rather than just numbers on a bathroom scale. Right?
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(14.01.b) cogito ergo sum confusus