Bitcoin Is Not a Pyramid. Coinbase Is.

In September 2016 I paid Coinbase $1,222 for two BTCs, $611 each. Seven months later, in April 2017, they paid me back $2,490, which was $1,245 for each BTC. My profit before tax was $1,268, over 100% of the investment, in just seven months. Moreover, if I had waited until today, I would have made $6,800 profit instead. Actually, I still have a few BTCs in my Coinbase account and I can make that 750% profit, if I sell now. Should I? The BTC price is over $4,000. Will it go up? Or down? What w...