ROI (return on investment)

Put in $10,000, end up with $13,000, and your ROI is 30%. The number is only meaningful with a time period attached: 30% over one year is excellent, 30% over ten years is worse than leaving the money in an index fund.

ROI also quietly ignores the cost of your time. A side business returning 200% on $500 of capital sounds spectacular until you notice it consumed 400 hours, which values your time at under $3 an hour.

Annualise before comparing anything. A 30% return over three years is 9.1% a year - final value divided by initial, raised to the power of one over the number of years, minus one - which is roughly what a global index fund does while you are asleep. Unannualised returns are how mediocre results are made to sound impressive, including to the person quoting them.

Then measure against what was actually available, not against zero. If the same money and hours could have gone into an index fund returning 10%, a project returning 9% lost money in the only sense that matters. Return on investment is a comparison or it is nothing, and the comparison has to include the thing you would otherwise have done.