If you know a guy who is a really decent, nice guy, but is a real jerk when he's drunk... and you come across him at some annual party, and he's drunk, and being a jerk... then what do you think about him?
Do you think, "He's a really jerk"?
No, of course not.
You think, "Ah, it's just the liquor."
We all know that alcohol and intoxicants change your biochemistry, how you act, and your personality. And we cut people a bit of slack for acting differently than normal on those sorts of things.
So... if you're able to cut Bob some slack for being a mean drunk, how come you don't cut yourself some slack when your biochemistry is off?
I woke in an absolute fog today, and had almost no willpower and was generally feeling a hazy fog. I was wondering what was wrong with me... until I realized I hadn't had caffeine. I took caffeine, and half an hour later I'm good.
This is obvious in the case of someone who has a mild addiction with withdrawal effects (caffeine, nicotine), but it's also true with diet, sleep patterns, and exercise.
If you're feeling low energy and run down, do you beat yourself up over it? Do you wonder why you're not doing more?
Or do you think, "Well, how's my biochemistry? How are the foods I'm eating, how's my movement and exercise, how's my sleep quality?"
For whatever reason, it's tempting to self-judge instead of analyze when we feel low and run down, and to extrapolate about our personality and work ethic and character. Biut to some extent that's nonsense -- you don't get mad a car for running without gasoline, you don't get mad at a lamp for not giving you light if it's not plugged into a power outlet, and you shouldn't get mad at yourself for feeling run down if you're not taking care of your biochemistry.
Next time you're low, take a quick scan through your mix of movement/exercise, eating, sleep quality, and other biochemistry. It's probably a tremendous part of why you're feeling the way you are.