When you have coins on an online exchange, it's not as if those coins literally sit there untouched. Your balance is just a number in a database. Similarly, if

When you have coins on an online exchange, it's not as if those coins literally sit there untouched. Your balance is just a number in a database. Similarly, if you deposit $100 USD(5 physical 20 dollar bills) in a bank those physical bills don't just sit there waiting for you. They can be given to anyone during the course of the business. You just get "100" added to some database row somewhere. When you want that $100 back, the Bank has to reach into its funds and pay you.