Those who suffered margin calls last night were all using leverage. Leverage equals borrowing money. In real life, borrowing money to gamble is unthinkable; people around you would say, "If you don't have money, don't gamble!" In trading, however, it's easy to be misled into borrowing money to open contracts. People around you would say, "Go all in! Borrow money like crazy and All In!"

Investing spare money is the most suitable.