Thesis drift
The position is still there. The reason you bought it is not.
Nobody decides to keep a broken thesis. They just answer a slightly different question each time they look, and the answer is always yes.
The definition
What thesis drift is
The paragraph worth quoting, and the reason it is not a knowledge problem.
Thesis drift is what happens when the original reason for owning a position stops being true and a new reason takes its place without anyone noticing the substitution. The holding never changes. The case for it is replaced piece by piece, each replacement reasonable on its own, until the position is being held for reasons that would never have justified buying it.
It is not a knowledge problem. Every investor knows to sell when the reasons change. It is an attention problem, and underneath that a record problem: you cannot notice a reason being swapped out if the original was never written down anywhere you would look again.
The sequence
One position, four reasons, eleven months
Each line was reasonable the day it was thought. Only the sequence is damning, and the sequence is the thing nobody keeps.
March
Bought
Utility-scale bookings grow more than 30% year over year through FY27.
July
Held
Bookings came in at 4%, but the backlog conversion should catch up next half.
November
Held
Management started buying back stock, so they must see something we do not.
February
Held
It is down 38%. Selling here would just lock in the loss.
The claim at the top is the only one that was ever testable, and it was settled against you in July. Everything under it is a reason to not act, arriving after the fact, and none of it would have persuaded you to buy in March.
The distinction
Thesis drift is not portfolio drift
Portfolio drift is mechanical. Your target was sixty percent equities, one holding ran hard, and the allocation is now seventy. Arithmetic caused it, arithmetic detects it, and rebalancing fixes it. Any brokerage or tracker will show you the number.
Thesis drift is about reasoning, and nothing arithmetic can see it. A position that has not moved at all, in a portfolio perfectly on target, can be held for a reason that stopped being true a year ago. The two problems share a word and share nothing else, which is worth knowing before you buy a tool for one and expect it to catch the other.
The defense
What makes it visible
Drift survives on the absence of a record. Write the original case as a claim with a number and a date, and the substitution has to happen in the open: the claim is either met or missed, the miss is dated, and a new reason for holding is visibly a new reason rather than the one you started with.
That is the whole defense, and it is unglamorous. Not a better forecast, not a sell signal. A record of what you believed, checked against what happened, kept somewhere you cannot quietly edit after the fact.
Which claim is worth writing down is the harder half, and it is on how to write an investment thesis. What to do on the morning one of them is settled against you is on when your investment thesis breaks.
Questions
Common questions
What is thesis drift in investing?
Thesis drift is what happens when the original reason for owning a position stops being true and a new reason takes its place without anyone noticing the substitution. The holding stays; the case for it is replaced piece by piece until the position is held for reasons that would never have justified buying it.
How is thesis drift different from portfolio drift?
Portfolio drift is mechanical: an allocation moves away from its target because one holding ran, and rebalancing fixes it. Thesis drift is about reasoning, so a portfolio perfectly on target can be full of it. The two share a word and nothing else, and a tool that catches one will not catch the other.
Why does thesis drift happen to careful investors?
Because every individual step is defensible. A second-order effect really might offset a miss, and management really might know something. Only the sequence gives drift away, and the sequence is the thing nobody keeps, so a careful investor reviewing a position sees one reasonable thought rather than the fourth substitution in eleven months.
How do you catch thesis drift?
Write the original case as a claim with a number and a date, before the position is taken, somewhere you cannot quietly revise it later. Drift survives on the absence of a record. Once the claim exists it is either met or missed on a date, and a new reason for holding is visibly new rather than a continuation of the one you started with.
Where {PRODUCT_NAME} sits
Solon keeps the record drift needs you not to have. You say why you own each position, typed or spoken, and it writes that down as named claims carrying numbers a filing can settle, then reads filings, earnings and rival moves against those claims and says when one is pressed. When you then decide to hold anyway, it keeps that decision too, next to the plan you set in advance.
The category is set out on investment thesis monitoring, and the comparison against the account you already have is on thesis monitoring vs. your brokerage.
Could you name why you bought your largest position?
If the answer has quietly changed four times, that is drift, and a written claim is what makes it visible.
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