There's a non-trivial chance that the Bitcoin bubble will burst because of some drastic event from Coinbase (or another exchange, like Binance). There is some incredibly suspicious activity going on there including:

- The fact that the coins land in your account weeks after you've purchased it (presumably to stop a bitcoin run?)

- Inability to pay their users.

- their exchange GDAX is known for having spoof buy and sell orders that disappear sporadically (this is illegal in regulated markets).

- the whole Bitcoin cash fiasco

I'm OK with speculating and bubbles, but not manipulation.