I have had friends who jumped into Bitcoin when they could not afford to lose that money and it almost put them out of business when the market sank. They were not thinking in the long run that they only wanted to make fast money and such a mentality almost always leads to panicking selling other times regretting decisions. The fact is that Bitcoin is more rewarding when patience is involved and you cannot be patient when your daily activities depend on how much you have invested. The discretionary income will give you that confidence to ride the storms without anxiety. What you invest is not the issue, it is only your ability to stick to it and be sure to withstand low points to receive the long term gains.