It's all relative. If $X is a lot to you, k^t * $X is even more. In forty years, the stock market has gone up about 30x, while the dollar has gone up a little b

It's all relative. If $X is a lot to you, k^t * $X is even more. In forty years, the stock market has gone up about 30x, while the dollar has gone up a little below 4x, meaning money invested would have really grown almost 8x. So if you can afford to squirrel away 1/8 of a meaningful amount, then it'll have been be useful to you when you're older. Sadly, a huge number of people can't do that. If your bills are $1000/mo and you earn $1001/mo, and invest the entire excess, when you're old, you'll have below $8 for every month invested today, which is meaningless compared to your expenses. 8 times nothing is nothing. But if your bills are $1000/mo and you earn $1130/mo and invest the entire excess, it'll entirely pay for a corresponding lifestyle when you're old. Perhaps a more important lesson in that case is compound interest on debt. If you borrow money from a credit card company, you can get exponentially fucked. The lesson may not be that compound interest gets you wealthy, but it's certainly that compound interest can make you worse than broke.