Lol wat??
You don't have to believe in fiat, it exists and it works for day to day transactions. Don't know about its future.
Yes, it is true that fiat is still the basis of the current economic system, but the past global crises had taught us to lose confidence in the current system, and it has strengthened our alternate ecosystem based on cryptocurrencies. Yes, fiat exist, but the mere fact of its existence does not make it reliable at all.