Say you bought 10k in Litecoin last week at $90.
And now it's $330... butttt.. because you can only buy 10k as an ACH transfer, your transaction hasn't posted yet. (Your price is locked in, it's just not in your account until the money clears from the bank)
So you should have a cool 25k profit but you can't sell yet.
When that transaction finally posts, what are you going to do? You're going to sell, maybe not all of it, but you're going to secure those profits. And that's going to cause it to plummet.
The people investing in Litecoin and driving the price up to $300+ do not believe in the product. They are weak hands that missed the Bitcoin craze, signed up for Coinbase and looked to get in on the next one.
That's why it plummets significantly by the end of the week.