@sussane, what you are describing is a very real concern.

There are two main buying statgies:

1. Buy low and sell high - This has the greatest reward, but you can lose out if you start freaking out.
2. Buy the same amount (in fiat) per month. This way your average purchase over the course of a set time frame will even out. This is great for a HODL strategy.

When emotions start running wild, we have to step back and take a few deep breaths.