i sell my BTC then waiting bitcoin price down again
i think we will down to $400

You sold all of them?
or did you hold onto some?
how long are you going to wait for prices to go to $400?
What if the price goes up?
At what point will you buy back in, if at all?
Do you have other investments? Did you put your BTC proceeds in the dollar or some other fiat?
They are good questions but that can be applied to each and everyone trading ^^
These are limits you put yourself. And lots of time they're rather shady, dependents on your state of mind and the moment!
Sure. Yet part of my reason for asking these questions is to attempt to get some meaning out of Proxiebuier's apparently vague post. Without some context, an amorphous assertion that a supposed person is selling BTC does not mean a whole hellava lot, and it might not mean anything to anybody else unless there is some meaningful context and further specifics in content.
In other words, the mere vague assertion comes off as kind of trollish because none of us really know very well the specific of others BTC holdings or diversification, except to the extent that they may provide us with some relevant details in line with the points they attempt to make in their posts.