Is it really the best way to invest your money?
Because of the way Bitcoin generates value or becomes more expensive, it could potentially lose all its value and became worthless.
Who assures you that this will not happen?
it depends on what you understand bitcoin as. I don't think that Bitcoin can just become worthless in future time without the signs indicating its irrelevant of future devalues.. some people kicking against that bitcoin is not an asset, so what is bitcoin, is very obvious that some asset become disvalue in reference time but it will take long periods such will happen.. using gold as illustration, before was threading in the market, but right now it has it limitations, because it potentials and firm has reduced because of existence of bitcoin, so before bitcoin can be worthless another thing that is greater than bitcoin will be into existence.