Bitcoin is a great investment but even the best investments can lose money if your timing is wrong, if you bought when bitcoin was 1000+ then even now you are still in problems if you timed your exit right you secured a good profit, so while bitcoin is in my opinion the investment of the century, you still need to use your common sense.
That is actually not something to be told if someone is wishing to invest money he should probably see everything before doing that, but still i think sometimes you don't know if this could happen, so if someone bought bitcoin when it was above $1k then he probably have thought that it will go higher but he did not think it will come lower later on.