Oh, because you know for sure that there will be a crash in the next 10 years? A prediction like that alone is worth billions, and I honestly doubt that you're different from the thousands of other who advocated for the same thing since the last 50 years.
In real life, an investor starts to keep assets that aren't as volatile but still aren't cash (e.g. bonds) as he approaches retirement. But even then, if they retire officially (i.e. at 65) then they probably have a national pension to draw from anyway.
> also, is Bitcoin a currency?
I don't care about cryptocurrencies at all, but it is the same classification as gold. People use it to speculate and reassure themselves thinking that "if it goes bad, it will preserve my wealth" and it doesn't have any value except when you trade it with someone for a usable currency.
Stocks tend to go upwards much more than cash, in the long term, even accounting for crashes. But those crashes are still big. IIRC, if you buy right after a big crash, you get about twice as much stock for the same price, and skip ahead 10 years (25% of the complete duration of the game) compared to someone who bought right before. I haven't run the numbers but I'm assuming that means it's worth holding only cash for 10 years if you're sure there will definitely be a crash some time in that 10 years. That's a best case scenario but 10 years of retirement is not something to be gambled lightly.
also, is Bitcoin a currency?