As of today (2021-02-25), 1 Bitcoin (BTC) is worth 50,863 US Dollars (USD). In comparison, 5 years ago 1 BTC bought you 416 USD. 
Imagine if there was a fictional country on the border of the USA, called "Bitlandia", that uses BTC as its official currency. Imagine we have a business person in Bitlandia who is selling a product to customers across the border in the USA. If that business personal was selling their product for 1 BTC:
Spotting this obvious problem affecting businesses in Bitlandia, the Central Bank of Bitlandia steps in, and starts to print currency in order to increase the supply of Bitcoins, and therefore reduce their value as they become less scarce. Gradually an equilibrium is restored, and our Bitlandia businesses can continue to trade is their BTC currency as it stabilizes.
By design however, this is not possible with BTC, as:
So you can now see the situation we have arrived at today: huge inflation in BTC price, and no mechanism in place to reduce that via an increased supply. The BTC price is getting squeezed up by demand-pull and cost-push inflation, AT THE SAME TIME.
As a business or as a consumer, using BTC to actually conduct transactions is becoming less and less attractive, when for example you are getting paid your salary in USD or EURO each month, and converting those currencies into BTC is prohibitively expensive at the current price.
Therefore as a currency for actually buying and selling goods and services in, day to day, BTC has failed.
So the logical thing to do now with BTC is to horde it. After all, why buy a pizza with something so valuable, when in one week from now you can buy five or ten pizzas for the same BTC amount? It no longer makes financial sense to spend BTC.
As an investor, if I bought 1 BTC for 416 USD five years ago, I would have an amazing return of 50,863 USD today!
As a speculative asset to buy and to hold, BTC is great for as long as the price goes up. Like any other investment, its risky.
But please lets stop calling it a currency, its not, its an asset.