Does anyone else forget why they bought a stock months later?

I had a weird moment with my portfolio last week.

I was cleaning up my watchlist and stopped on a stock I bought about six months ago. It was up around 20%. Not bad. And I genuinely could not tell you why I bought it.

Was it industry growth? Competitive advantage? Some catalyst I was expecting? Or did I just see someone mention it and figure "eh, why not"? I have no idea. Price, cost basis, percentage gain — all right there. Reasoning? Gone.

And here's the thing: it's not about the money. It's that I realized I have zero memory of my own reasoning. Which means I can't tell whether I made a good decision or just got lucky.

That's the part that bugs me. When a stock goes up, my brain conveniently assumes I was right. When it goes down, I start wondering if I was wrong. But neither reaction is based on anything real — because I can't remember what the logic was. I'm basically judging my past self without any evidence of what past me was thinking.

It got worse a few weeks ago when the stock dipped and I found myself debating whether to sell. Hold or sell? I had no framework for the decision. The numbers just said "down 5% this month." That was it. I might as well have been flipping a coin.

It's like being a student who remembers the answers but not the formulas. Works until the questions change.

I review my portfolio all the time. I check prices, I track performance, I obsess over allocation. But I almost never review the actual decision — the "why." And I'm starting to think that's the only part that matters for actually getting better at this. The return tells me the outcome. The reasoning is the only thing I can learn from.

A few questions for the thread:

1. Do you track your investment thesis? Like, actually write it down somewhere?
2. How do you remember why you bought something?
3. Do you ever go back and review old investment decisions? Not the returns — the reasoning.
4. If you do any of this, what do you use besides spreadsheets?

Honestly curious how other people handle this.

Since it kept happening to me, I started experimenting with a simple investment journal. Nothing fancy — basically a note to my future self before I buy something. It captures:

- What I bought and at what price

- Why I'm buying it (the actual reasons)

- What I expect to happen

- What would prove me wrong

Plus a reminder to come back and review it later.

To be clear: it's not stock prediction, not trading signals, not AI picks, none of that. It's just a way to make my decisions checkable instead of having to guess what I was thinking months later.

Honestly, I'm not even sure it's worth the effort yet. I've only been at it a few months. But the few times I've gone back and read my old notes, it's been eye-opening — especially the parts where I can see exactly where my reasoning was sloppy.

I'm trying to understand whether this is a problem other investors have, or if it's just me. If you've solved it differently — a journal, a checklist, a rule you made for yourself — I'd love to hear how.

Some people asked about the experiment, so I put a simple early version here: https://landing-page-seven-iota-50.vercel.app/