The costliest investment mistakes rarely come from ignorance. They come from decisions made under the sway of emotion: selling in the middle of a crash or buying out of euphoria. A written plan is a promise to yourself, drafted in cold blood, that you reread when the market gets agitated.
Why write it down
A mental plan gets distorted. You remember your rules when all is well and forget them when they become uncomfortable. A dated document cannot be reinterpreted: it reminds you of what you decided before the panic. It also helps you measure your results against a goal, rather than against other people's performance.
The elements of a plan
- Goal: what are you investing for (retirement, a project, passing on wealth) and for roughly what amount?
- Horizon: in how many years will you need this money?
- Risk capacity and tolerance: what fall can you bear, financially and psychologically?
- Target allocation: the split between shares, bonds and cash, with ranges.
- Investing rhythm: regular contributions, amounts, frequency.
- Rebalancing rules: how often, or at what deviation, do you act?
- Exit rules: in which cases do you sell? A change of goal, never a security falling on its own.
- What you will not do: leverage, products you do not understand, decisions based on a rumour.
Plan extract (fictional)
“I am investing to supplement my income in 20 years. I contribute €300 a month. My target allocation is 70% shares and 30% bonds and cash, with a tolerance of plus or minus 5 points. I rebalance once a year. If my portfolio falls by 30%, I do not sell: I reread this plan and wait 30 days before any decision.” This text is an illustrative template, not a recommendation.
Ask yourself honestly how you would react to a 30% fall in your portfolio. If the answer is an urge to sell everything, your allocation is too aggressive for you, however sound it is in theory. A good plan is one you stick to, not one that is optimal on paper. Reread it once or twice a year, and at every major life event: a change of job, a birth, a property project. Revise it when your situation changes, not when the markets change. Finally, keep a small journal of your decisions: noting why you acted helps you spot your own reflexes.
The waiting-period rule
Impose a cooling-off period (a few days) before any decision that departs from the plan. Most impulses fade faster than markets turn around.
Key takeaway
- ✓A plan written in cold blood protects against decisions made under emotion.
- ✓Goal, horizon, risk tolerance, allocation and action rules form its core.
- ✓Revise it when your life changes, not when the market gets agitated.