Why not buy one bitcoin today? If it falls to $600 you buy one, at $500 you buy one. And so on. Your average buy would be ~$ 633. So you don't have that much lost(%). If you bought one bitcoin today and it wil start to rise to $2,000 you don't regret. If it keeps falling you can buy with fiat to make your average buy <<.

Just make a plan. And if you believe in Bitcoin this is the best investment strategy.