Let me share something I only understood after losing a lot of money.

Three years ago, I bought AMD. I read a ton of analyses: the P/E ratio was reasonable, it benefited from AI, there was a technical breakout—all the logic was right. After I bought in, it dropped 30%. I always thought it was my misjudgment, but later I realized it wasn't—that quarter, Vanguard was quietly reducing its position, and I had no idea.

Institutions don't announce when they reduce positions; it doesn't make the news, but it happens. By the time the 13F data comes out, it's already too late.

After that, I started seriously researching institutional holdings. Honestly, it was really painful at first. The SEC's EDGAR website looks like a relic from the last century. 13F files are in XML format with hundreds of lines of data. I manually sorted through it in Excel a few times; my eyes were blurry afterward, and it still might not have been right.

Later, I started using Longbridge Skill. The longbridge shareholder feature directly shows the top ten institutions and their position change data, and longbridge investors lets you check the changes in an entire institution's portfolio. The first time I ran it, I was stunned—something that used to take two or three hours was done in 30 seconds.

But the tool is secondary. What really made me think clearly was one question: Why are institutions buying at this price?

I can deduce their cost basis for building the position, and I can calculate the gap between the current price and that cost. If an institution built a position at $80 and it's now risen to $120, their floating profit is already substantial, and they could reduce their position at any time—if I jump in now, who's on the other side of the trade?

Conversely, if the stock price falls back near the institution's cost basis, they're likely to continue holding or even add to their position. Support at that level is more solid.

I'm not saying that following institutions means you won't lose money. Institutions can also misjudge, and they have their own funding pressures. But at least now I know what's in the water; I'm not swimming blindly in the dark anymore.

Last month, during that TSMC rebound, I checked in advance that both BlackRock and Vanguard had added positions at low levels. I held without panicking, and it went from $326 back up to $444. Maybe it was luck, but I think it was more about having confidence.

The fundamental reason for not being able to hold a stock isn't a lack of willpower; it's a lack of information.