You can be calm when the market falls or may sell using margin trading. Why not? I personally think that it is also a good idea. However, you need to analyse first, as any fall may be a part of a brief correction:)
being calm when the market falls is very good, but it's very difficult to get that kind of thing, because basically when you're holding a coin, or other asset, you definitely won't calm down and be in a hurry to sell it.