Investing in bitcoin is not foolishness. People who invest are taking risks because of the possible returns that they are going to earn in investing in bitcoin. They can also get some profits if they trade with bitcoin.
When you make such a purchase - a purchase that you should never have made - you are speculating that it is not a useful and productive activity. You enter a psychological adventure, where your only goal is to win the battle against other people. Even if you win some money because of blind luck, you will lose some time and vitality, which means that you will lose.