Dumbest? That's a tough one. I don't think of lack of knowledge as "dumb", especially when you still "don't know what you don't know", and I don't class losses incurred through that as "dumb" - just a tuition fee while you're learning. Technical errors, or those mistakes in execution that I made early on, go in the same bucket.
Having said that: I've been exceptionally lucky - or perhaps, like Hume, have proportioned my belief in my trades to the evidence - so that my losses to "dumb shit" have been unpleasant but small (the money meant little, but being stupid
hurts). A quick review of those "ouch" trades - and you can be certain I
remember them - tells me I lost less than $3k total in those.
(And - no, you can never "make them up". All you can do is remember them - preferably as a
class of mistake - and avoid them in the future.)
Analyzing the common factor in "dumb shit" tells me it happens most often when I use emotion instead of rational factors to make decisions. Whatever other problems exist are too small to be seen behind that one. I've managed to reduce that class of problems by a huge factor... but I won't say that I'm done with it forever.
Some examples:
I believed - even though it seemed too good to be true, and I
knew that at least half of that belief was hope - TradeStation's P&L figures after "rolling" the trade I had. Upshot: the "gain" it showed was only for the "rolled" position - NOT the sum total for the trade from the beginning. These days, I keep a spreadsheet of my own.
I was learning a directional strategy - one that actually works reasonably well - and assumed (hoped) that I understood it well enough to predict the movement of several stocks for a couple of weeks ahead. Ooops. Upshot: these days, I use it as a tool that helps me construct a market narrative - not as a magic wand.
I've exited winning trades far too quickly - usually while watching a
long red bar - instead of sticking with my original prediction for them. Upshot: having learned that "video game"-style trading isn't for me, I don't do fast-paced day trading anymore - and lean into my tools (market profile, market sentiment, $TICK, etc.) to give me a picture of what the market is doing. It's not perfect, but it's not "
ohshitohshitohshit I'm gonna lose everything I gained", either - and I'll take those calm, rationally-based wins and losses. (Gamma on flies as they approach expiration is still pretty batshit, though.

)