Monitoring an investment thesis

In simple terms

Buying a share is the start of the work, not the end. The business keeps changing, and so does the evidence about your assumptions. Monitoring means regularly checking whether the thesis still holds, updating your estimates honestly, and acting when it does not.

A quarterly routine

When a company reports, spend an hour on a fixed routine:

1. Read the results and management commentary, as the earnings season lesson explains.
2. Update the tracking table with the key drivers.
3. Check each key assumption, kill criterion and milestone, as the proving you wrong lesson describes.
4. Scan exchange filings since the last check: shareholding, pledges, insider trades, rating actions, important announcements, as the exchange filings lesson explains.
5. Write two or three sentences: what changed, and whether the thesis is intact, weaker or stronger.

A tracking table

Updating estimates

When evidence changes, update your assumptions and scenario values, as the scenarios lesson explains, in both directions. Common traps:

• Updating only when news is good.
• Explaining away each weak quarter as a one-off, until the one-offs become a trend.
• Raising the bull case to match a rising share price without new evidence.

The purchase price is irrelevant

Once you own a share, the price you paid becomes a powerful anchor. Investors hold losers "until they get back to what I paid" and sell winners "to lock in gains", as the behavioural biases lesson explains. The market does not know your purchase price.

The right question is always: given what I know now, would I buy this share at today's price? If not, there should be a good reason to keep holding.

Triggers for a full review

Some events deserve more than a quarterly check:

• A kill criterion is met or a milestone is clearly missed.
• A large acquisition, a new line of business or a major capital raise.
• A governance warning: auditor resignation, senior departures, rising pledges, related-party surprises.
• A large change in the share price without obvious news, which may mean others know or fear something.
• A change in your own circumstances or portfolio.

A full review means going back through the research process, as if researching the company afresh.

Not too often

Monitoring is not watching prices daily. Checking too often encourages reacting to noise, as the emotional decisions lesson explains. A quarterly routine, plus reviews triggered by real events, is usually enough for long-term investors.

Why it matters

Theses break slowly and then suddenly. A simple routine catches the early warnings while there is still time to act calmly, and keeps you honest about whether your original reasons still apply.

Limitations

Quarterly data is noisy, and some problems only become visible late. Monitoring takes time, which limits how many companies one person can follow well. Judgement is still needed to tell temporary setbacks from lasting change.

Common mistakes

• Treating research as finished after buying.
• Anchoring on the purchase price.
• Explaining away a series of weak quarters.
• Reacting to daily prices instead of evidence.

Try it yourself

1. For a share you own or follow, build a tracking table of four to six key drivers.
2. Fill it in for the last four quarters from results and filings.
3. Write a two-sentence status for each quarter.
4. Ask whether you would buy the share at today's price, and write down why.