Hindsight bias is a term used in psychology to explain the tendency of people to overestimate their ability to have predicted an outcome that could not possibly have been predicted. In essence, the hindsight bias is sort of like saying "I knew it!" when an outcome (either expected or unexpected) occurs - and the belief that one actually predicted it correctly.
Arbitrage is the purchase of a product which is then sold to make a profit. Successful arbitrage relies on the fact that different markets value products at different rates. It’s popular in the stock and commodities market, and is the driving force behind a number of industries from antiques to cryptocurrency. A person who uses arbitrage is called an arbitrageur.