What causes the price of bitcoin to always decrease? If the price goes up just a little later falls again, and will bitcoin when december go up or even fall deeper?
It is not always going down. Sometimes it goes up, like a month ago or so bitcoin prices went above $8,000 and it was party time for everyone here and everyone started to start topics about how "bitcoin is going to $50,000 at the end of the year", lately it has gone down again to $6,000 levels and now people are afraid that it will go down to $4,000 or so and now we are seeing how people think "bitcoin always decreases", it is not.
You need to see how bitcoin moves, it does not move sideaways it moves up and down, sometimes it goes down you are right however sometimes it goes up as well, it doesn't stay at the same number for a long time, specially comparing to other investment methods it has a lot more upside than downside.