in 2013, 84-year-old jack bogle gave investors a rule that sounded almost too simple: keep 95% of your money boring and give yourself 5% to do whatever you want. bogle knew many investors would eventually want to pick individual stocks, trade the market, or chase the next big idea. instead of pretending those urges didn't exist, he suggested putting that money into a separate "funny money" account and keeping it to no more than 5% of the portfolio. the other 95% belonged in what he called the "serious money" account, built around long-term investing and left largely alone. bogle's point wasn't that the 5% was going to make you rich. it was a way to keep a little speculation from turning into a problem for the rest of your portfolio. "guess on funds, guess on markets, guess on stocks if you want to,” he said. “they will hurt you a lot." he even suggested leaving the speculative money alone for five years and then comparing the results with the serious-money account. bogle said he would be surprised if at least 95% of those speculative accounts didn't do worse. the idea was surprisingly practical: if you know you're going to feel the urge to make a bet, give yourself a small amount of money where being wrong won't change your financial future. the rest stays boring. and that was exactly the point. the full bogle interview is in the video below.