Before, I couldn't understand how you could possibly make money on something going down in value.
You borrow my shovel. Sell it for $25. You then go to Home Depot and the shovels are on sale for $14.99. You spend 15$ to replace my shovel and keep the $10.00 left. Now replace the word "shovel" with "share" and multiply by 100 or more.
reddit. (I fleshed it out a iittle bit:)