I don't understand

Hi everyone, first of all I'm sincerely sorry for poor English, since I'm French I was to busy eating frogs to learn English.

I'm interested in btc, but I actually can't really invest nor save money (21 yo student).

There is something I don't really understand about btc and cryptos : I read a lot that "regular" money (such as dollars, euros... fiat money if I got it right ?) is going to disappear and only cryptos will remain, then btc will be worth 10.000.000$ and everyone in this sub will be extra rich (keep some for me)

I don't understand how btc can be that high if it becomes the new regular money. A water bottle will cost 0.0000002 btc ? Isn't that weird ? Thinking that way, I'm sure that btc will be ~1$ when fiat money will be gone.

Am I the dumbest being alive ?