A very low cost index fund where you don't put in all your money at one time ... If you accumulate a low cost index fund over 10 years ... with fairly regular sums, I think you will probably do better than 90% of the people around you that take up investing at a similar time.
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(quote at 2:24:01 of 2:33:25. This is often quoted online as: "If you invested in a very low cost index fund — where you don't put the money in at one time, but average in over 10 years — you'll do better than 90% of people who start investing at the same time.")