I keep missing my goals as a solo founder — not because I don't execute, but because I execute on the wrong assumptions

I've been building things on my own for years, and I've noticed a pattern that keeps killing me:
I don't fail because I don't work hard. I fail because the picture in my head doesn't match reality — and I usually don't find out until I've already sunk weeks into it. Then I have to backtrack, re-adjust based on what the market actually told me, and start again. Over and over.
The painful part isn't the wasted time. It's that the wrong assumption always felt completely reasonable before I tested it. And with no co-founder or team, there's no one to stop me and ask "wait — why do you think this will work?"
So I started building something to fix this for myself. The idea is a tool that acts like the co-founder I don't have — one whose only job is to sharpen my decisions. Roughly three things:

Before I act — it helps me lay out what I'm actually trying to achieve, and surfaces the hidden assumptions baked into my plan, so I don't run on a blind spot.
After I act — it reviews with me: where reality diverged from what I expected, and what I should actually learn from that (instead of just "it didn't work").
Then — it helps me decide the next move based on what I just learned, so each attempt is smarter than the last

The core isn't doing the work for me. It's helping me make better decisions and not waste weeks on the wrong direction.
I'd genuinely love your honest take, especially from other solo builders:

Is this a real problem for you, or just a me problem?
How do you currently deal with it — do you have a system, or do you mostly just go with your gut and hope?
If a tool actually did this well, is it something you'd use? Be brutally honest — "no, because X" is the most useful answer you can give me.

Not trying to sell anything here — it's early and I genuinely want to know if I'm building something real or just scratching my own itch.