Generally we know that every choice we make in life is risky and none of it is certain to give us our desired result regardless of how sure we are with the choice we're making. Even when you're investing in yourself by learning a skill or getting the normal education, we all know that sometimes after learning those skills and or getting the required educational qualification, it doesn't mean that it's 100% guaranteed that we're going to be successful at it. In the context of investing into Bitcoin, though we have faith in bitcoins future, that doesn't in any way suggest that we don't know that things can go wrong and Bitcoin will become a thing of the past. These are just some of the reasons why you see people talking about investing what you can afford to lose while you're making any investments. It's not as though they are anticipating any losses but if you're going into anything without counting the cost which in most cases involves considering the possibility of loses, you get fooled to invest blindly.

Note that even when you buy a property or establish a reputable business, it's not 100% certain that the business will not crash. Event do happen and the land you've invested all you've got into goes out of your reach and what do you do at that point? The reason why people diversify there investment choice is to place themselves in a position where they aren't risking too much. If you see opportunity in an asset, it's not out of place to invest huge into it but you don't go about the investment with all that you have or else it becomes almost 100% gambling and when anything goes wrong, it hurts you to the peak.