11/02/2026
Overconfidence in investing is rarely a matter of believing the impossible. It shows up instead as ranges that are far too narrow.
Alpert and Raiffa asked people for ranges wide enough to be right 98% of the time, and the true answer fell outside those ranges roughly 40% of the time. The estimates were not wildly wrong, though the confidence attached to them was.
The financial version appears whenever a plan rests on a single figure: an expected return, a retirement date, a sale price for a business.
Consider a household planning to sell a business in five years at a particular valuation. A plan built on a range, with a stated response at both ends, survives being wrong.
Write the prediction down with a date and a range rather than a point, then keep the page.
Where in your plan does a single number carry more weight than the evidence behind it?
For more on planning with ranges rather than single figures, visit Solinvest.ca.