In order to sell something someone have to buy it. But what happens if there are no buy order at $2000.
On most exchanges, the order type is limit order by default. If bitcoin is at $20000 and you place a sell order at $2000. As you want to sell at lower price, the market would be filled at $20000 immediately, which is the market price of bitcoin.
Edit:
Let me explain it better
Bitcoin at $20000 for instance
If you want to buy anything at higher price, people will want to sell
If you want to sell at lower price, people will want to buy
Buying bitcoin, the order would be filled at exact or higher bitcoin price (the price you set)
Selling bitcoin, the order would be filled at exact or lower bitcoin price (the price you set)
Assuming bitcoin is at $20000, you want to buy and place to order at $19999 or lower, no one would want to sell. Order will not be filled.
Assuming bitcoin is at $20000, you want to buy at $20000 or higher. The order would be filled immediately
Assuming bitcoin is at $20000, you want to sell, and place order at $20001 or higher, no one will want to buy. Order will not be filled.
Assuming bitcoin is at $20000, you want to sell at $19999 or below. The order would be filled immediately
You're right and to further simplify this for you, let's bring it back home and assume you're buying from a regular market, you must first, know that both the buyer and the seller would want to make profit at every given time and none of them would want to deliberately make loss or buy a commodity at a higher price when the same commodity with the same value can be bought from another generally known market at a more lesser and generally accepted price.
For instance, if the general market price for a biscuit is 50 and now you want to buy the biscuit for lesser price of 49, it will be so difficult to get a seller, but if you want to buy same biscuit at a bit higher price from the market price, let's say for 51, you'll immediately get a seller who will want to seller and make an extra profit of 1. And also the reverse is the case if you want to sell as well.