Joe here...
I know what you're asking, why are you asking about Christmas... it's not even June yet? We have 6 1/2 months until then.

True. However, as many of us want to see a return on investment, we must be concerned about Christmas right now. In truth, the end of the year is the enemy for us, that is for those of us that wants Bitcoin to continue on to reach the $1m price.
The beginning of 2017, Bitcoin started in value at $1017 USD. On December 16th, it reached $19,187 USD. This time two years ago, it was at $1782. While we have seen a lot of really big highs in it's history, this high of nearly 20k, in my opinion, started around this time that year. It reached a new height and people started to take it seriously. We saw another big push August 1st, and another near the end of September. But the BIG wave started on Veteran's Day, and blew all expectations. And then it dropped. We haven't even been close since then.

In 2018, we saw a continual drop in price, but the major drop of the year happened right before Thanksgiving. Coincidently, on Veteran's Day. It appears that day is very important for Bitcoin, the time before the holiday's really hit. Well, if we see a repeat of 2017 (as some recent highs suggest), we're going to see some big pushes in the coming months, and by the end of this year, we may see $20k USD again, or higher. The question is, what happens then?
The end of the year is a time of celebration, a time of joy, a time of giving, and remembering the greatness of year before. It's a time of trying to fulfill obligations to customers, to family, to shareholders, and to our pockets. Basically, it's a time of manipulating money.
For the Schmos and Smucks, we need to buy presents and trees and dinner. Everyone wants to celebrate beyond their means, as if they are richer than they actually are. We pray for financial bonuses and take advantage of the holiday sales. More than that, we want to have money for ourselves. Nothing wrong with that. If I had invested $1000 in January 2017, by December 16th, it would be worth 19 times its value, or $19,000. You better believe I want a chunk of that, for the best Christmas ever and to maybe pay some bills or having a few extra things.

For the big businesses, the end of the year means trying to make your business appear that it's made a profit. Many companies will spend a lot for the holiday season, and maybe they even do well, but not as much as they desire. So, cut a few employees loose, and do some tricky things on paper to show your shareholders that in the grand scheme, your year-end profits are good. This is how businesses work. If they can't do that, they need to get the money from somewhere, why not sell off some assets.
Then we have the whales, those who either had a lot of disposable income to buy a large amount of coin, or those who had obtain Bitcoin when it was worthless. If I had obtained 100 bitcoins when they were valued at $1, at it's height, it's worth $1.9m. Let's sell a good chunk of that and buy a house, or two houses, and a car.
The end of the year causes us to need money, as much as we can get. I'm not here to judge what anyone does with their money, but to explain why the value dropped from ~20k to ~3k in over a year. End of the year is brutal, and there is good chance that we will see Bitcoin get to a high value, but will it survive the Christmas season?
It can, if we can convince people not to sell. Easier said than done. A Schmo like me, I got less than $200 in right now. If I could put more in, I would (and likely will many times between now and the end of the year). If it hits $20k, then my coin will be worth over $600. Not enough for me to pull out, unless the holiday season demands a lot of me, and then I will try to keep as much in as possible. At $50k, my value will hit over $1600. Yeah, then I might take out money, because I really need it. If I do so with a lot of others doing the same, the value will drop again.
The other thing is, if we know it's going to drop at the end of the year, shouldn't we sell to get the highest value. What if in 2017 I decided to wait until it hit $20k or decided not to sell at all... what value I would have at that time and riches I would be awarded, was all lost. That is defeating. Knowing it could happen again, shouldn't I then sell when it gets to $20k, no matter what? And of course, once the price starts dropping, we feel more encouraged to sell, just so we can get our son the GI Joe with Kung-fu grip. Remember that scene from Trading Places:
So why are we worried about Christmas? Because we need to make some hard decisions as individuals and a community on what we will do at the end of the year. If we ban together and keep our coin, then we can reach to higher amounts as the years go on. If we scatter and do what's only best for ourselves, then it is likely that as we saw in 2017/8, the Bitcoin market will crash again.