Question about investing in Bitcoin only what one can afford to lose

Hi everyone,

Simple question - if Bitcoin is a life jacket or hedge against all sort of issues with fiat currency then why there is always a disclaimer that one should invest only what they can afford to lose?

I understand the term "stomach volatility" as so far no matter how deep Bitcoin ever plunged it still goes up.

However, the term "only invest what you can afford to lose" sounds like there is a chance it will go to zero.

I, personally, can undergo the former, but the latter stops me from going all in.