On what basis do you assume it will fall?
I mean it has not fallen that much yet. I doubt it will go lower that 7000$ now.
There could be many reason to rise and fall.
To Rise:
1. Demand High and less supply.
2.Out of 2.1 million 1.6 million already in market. so remaining is very less.
3.Its decentralized , so no one has control over it.
To fall:
1. So may people can buy in low rate . if price never go down then only few people have these cryptocurrency .
once price will go down many people can invest.
2. More people more popularity.
Add here if i missed something.