Recoveries
Your investment goes down 30%.
You had $100, now you only have $70.
Tough luck.
What's worse, though, is that to regain it, you need a return of not only 30% but more than 42%.
Warren Buffett gave two rules of investing.
Never lose money
Never forget rule one
Once you've lost your investment, it's exponentially harder to regain it.
See the Barbell strategy and the Kelly-Criterion to effectively avoid this situation.