Buy when everybody is pessimistic.
We might not be there yet but it's close.
I'm still living in Bitcoin euphoria, since the CFR took an interest in Bitcoin only 2 of the 4 big predictions have come to pass.
1) the collapse and or outlawing of key exchanges
2) the arrests of known Bitcoin personalities
3) a media smear camping demonising Bitcoin.
4) a collapse in the price. (I'm still coming to terms with Bitcoin leaving double digits)
To be honest the only thing that can collapse the price IMO are the week hands, (non believers) stolen Bitcoin and whales redistributing/ facilitating future wealth growth, and I think a lot of coins @ the new order of magnetude have already been flushed.
I welcome a drop but if it happens it may take time or if it is quick it will kick some new big players in the balls, if it happens.