If a day we see the Bitcoin value at $20,000 people will start to sell everything they own. Only the traders and the longtime Bitcoiners will continue to hold. And since the majority will be selling the price will drop in a short period of time. And the circle will continue, once at $20k again the same thing will happen.
I think you can forget the $50k

Of course.Its true.But donot forget that even if most people sell their bitcoins when it's price reaches 20,000 dollars,still if more new investors come in to the bitcoin market then it's price may remain at that same range.