Invisting bitcoin is not foolishness but makes you earn a lot of money. Every investment involves some degree of risks, you must read a lot and do your own research before investing as well. Taking a risk by investing in bitcoin does not seem foolish to me in anyway
There is no foolishness when investing bitcoin that will results to a good profit at the end. But sometimes we take the big risk in investing bitcoin because the price is unpredictable and no ones knows when the price is going high and going to low, but having with great patience will surely surpass the volatile behavior of it. Then there is no foolishness seen by doing like this at all.