Trading cryptocurrency queries

[jpawesome78]

All these cryptocurrencies tend to have a up and down phenom, my I ask the oldies here if what could be the reference for a coin for it to increase its value, and decrease at the same time.

Deur, Bithire has dramatically decreased its value.

Ethereum, radium has dramatically increased its value.

and some come has a fluctuating 10-90% up down flow,

My question is what do determine this changes, how and why?