Trim vs cut: two very different decisions
Selling part of a position and selling all of it look similar from the outside. They are opposite decisions based on opposite diagnoses.
TL;DR — Selling part of a position and selling all of it look similar from the outside. But they are opposite decisions based on opposite diagnoses. Confuse them and you will either stay too long in a losing idea, or sell your best investments right before they run further.
Every time you want to reduce a position, start with one question: is the original reason I bought this still true? If yes, you trim. If no, you cut.
Trimming is for when the thesis is intact but the position has grown too large. Say you bought an energy ETF at 15 percent of your portfolio, and it ran to 28 percent after a big oil price move. The macro regime that made energy attractive is still in place. The position just overshot its target size. You sell the excess back down to your target (say 15 to 20 percent) and keep the rest running. You are not leaving the position. You are rebalancing it. The profits go back into positions that are below their target, or sit as cash temporarily.
Cutting is for when the underlying thesis has broken. The macro regime changed. The country moved into a recession when you expected growth. The central bank reversed its policy. The structural demand driver that made this interesting disappeared. In this case, you do not trim. You exit fully and redeploy the capital somewhere with an intact thesis.
The expensive errors go in both directions.
The trim-when-should-cut error: a position keeps falling. The original thesis clearly no longer applies. But instead of exiting, you tell yourself you are "just managing the size." You end up with a shrinking position in a dead thesis, still dragging on the portfolio.
The cut-when-should-trim error: a position has run 80 percent in a year and you feel nervous about the gain. You sell everything to lock it in. The macro regime is unchanged. Three months later it runs another 50 percent and you missed it. "This has run a lot" is not the same as "the thesis is broken."
A simple test before any sale: write down in one sentence why you originally bought the position. Then ask: is that sentence still true today? If yes, trim only if it is too big. If no, exit fully.
Example — An investor holds a Latin America ETF at a 10 percent target. It runs to 22 percent over a good year. The regime is still intact (growth phase, strong currency). They trim back to 10 percent, bank the gains, and keep the core position running. A year later, the country moves into a recession and the central bank starts a currency defense operation. The thesis is now broken. They exit the remaining 10 percent fully. Two different decisions. Two very different reasons.
One question decides everything: is the original reason still true?