Nobody really explained or discussed the hard cap.
A project has a maximum number of coins or tokens. The developers can't create more coins, although they can split the total amount of coins into portions. A portion for public sale, another for salaries and expenses, a portion for marketing, etc.
Let's say a project has 100 coins. 50 coins are reserved for the public sale. Each coin is $1. The hard cap is 50 coins = $50.
But why would you limit your project to a fixed amount of money? You could also develop a scheme where each sold coin increases the price of the next coin, up to a just shy of infinite hard cap.
Coin #1 = $1
Coin #2 = $2
Coin #3 = $4
Coin #4 = $8
Coin #10 = $512
Coin #15 = $32,768
Coin #20 = $524,288
Coin #30 = $536,870,912
Coin #40 = $549,755,813,888
Coin #50 = $562,949,953,421,312