On self-worth and self-doubt

Something happened yesterday.

Well, 2 something, a great and a not so great.

Guess which one kept me awake? Which made me clench my jaws so tight I pulled a muscle in my neck and could not open my mouth to speak or eat until now (that might have been a bonus, though)?
You guessed right.
But why is it that even when I receive wonderful news - which included signing with a new client to whom I was warmly recommended by another one and a subsequent new interesting long term assignment - I could not focus on it?
Instead, I reread a dissatisfied client's email, about a #translation reviewed internally and sent back to me as being "full of mistakes".
No matter that the "mistakes" were 1 typo and 7 preferential changes in style and tone (which could have been prevented if they had provided me with proper instructions).
No matter that I addressed their issue immediately.
No matter that such a situation only happened to me once before.
No matter.
I still spent my evening doubting myself, awakening the old demon-friend Mr #ImpostorSyndrom and his cohort of self-pity, tiredness and heartbreak heading the convoy.

And I keep wondering: why is it that finding the #RightBalance between what we know is our #selfworth and the sad marginal incident is so damn hard?

Have you experienced this as well?