Invest with the amount of money that you can afford to lose only means that what you want to invest on is highly volatile. That helps you to know how risky it is in what you want to invest on.

If you invest big and you make huge amount of money, that is your luck. Or you invest hugely in it and you lose, that is it. But you know already that you are dealing with a risky asset.

You should know how risky what you want to invest in is, research about the asset to know if that statement is entirely true or not, some investment are not that risky, while some are very risky.

Like bitcoin, when the price decreased so significantly, you know you have more precentage in success rate, unlike when the price is high.

About altcoins, you know how gambling they are.