And why Litecoin is going to have a great run in 2018. In order to answer this question, we first need to dive back into the basics of the bitcoin protocol.
How are new bitcoins created?
It's no secret to anybody involved in cryptocurrencies that bitcoins can be mined. While the whole topic of mining cryptocurrencies deserves a dedicated article, for now we just need to know that you burn energy, in the form of having GPUs or ASICs use electricity for hashing, in order to package bitcoin transactions into neat blocks. The one miner that manages to be the first to produce such a block and broadcast it to the network gets a reward - a certain number of bitcoins. Here's what Satoshi Nakamoto has to say about this in bitcoin's whitepaper:
By convention, the first transaction in a block is a special transaction that starts a new coin owned by the creator of the block. This adds an incentive for nodes to support the network, and provides a way to initially distribute coins into circulation, since there is no central authority to issue them. The steady addition of a constant of amount of new coins is analogous to gold miners expending resources to add gold to circulation. In our case, it is CPU time and electricity that is expended.
In reality, it's not a constant amount, but a variable amount. Bitcoin started off with blocks that are easy to mine (low difficulty), and high rewards, at 50 BTC per block mined. However, the more blocks are available, the smaller the reward that miners receive. Right now, blocks are hard to mine (increased difficulty, more energy needs to be spent to find one), and the reward gets smaller - at 12 BTC per block mined currently. What this means is that we've got two factors working simultaneously: increased lower bound for bitcoin price, since it's harder to mine, you need to spend more energy, and thus you won't sell your freshly mined bitcoin for a price that's lower than what you had to spend to mine it; and increased scarcity, as there are fewer and fewer new bitcoins being produced every day. These two factors, combined with the ever growing demand, are what makes bitcoin appreciate in price so significantly.
How has bitcoin halving impacted price in the past?
There have been two bitcoin halvings to date: in 2012 and in 2016. In both cases the prices seemed to stabilize right before the halving, in anticipation, and when the actual halving hit people went wild in the news how that didn't have any impact. What really happened though is that miners started selling their coins at a higher price, but hoarders were happy to convert a portion of their BTC portfolio into fiat. As soon as hoarders sold out of what they were comfortable selling, there were no other options than to buy from miners.
The 2012 halving has sent bitcoin from $20 range to $240 in April '13, with a lag of 6 months, all the way to $1000 in December '13.
The second halving was in 2016. You can still find articles by skeptics saying that this didn't mean a thing and won't impact the price whatsoever. Fast forward one year, and bitcoin has moved from $600 to $5000.
The third halving is coming in 2020, and the prices are rallying up to at least $10000, more likely to $30000, by late 2019, where they will stay until the halving happens. We have quite a bit of bull market left!
Why do you keep bringing up litecoin?
That's a very good question. To tell you the truth, I've dismissed litecoin as a useless fork up until this August. You can argue that today's bitcoin is the original bitcoin, with Bitcoin Cash being a chinese knock-off, but if another fork for SegWit2x comes along some time this year there won't be much of the original bitcoin left. This would, essentially, make litecoin the oldest bitcoin fork!
Unlike bitcoin, litecoin has clear leadership in Charlie Lee, which is crucial for a rapidly developing industry, who makes sure there won't be any litecoin hard forks. Litecoin is more decentralized since it's hashing algorithm is ASIC resistant. This means that you don't need to buy dedicated expensive proprietary hardware to mine it - you can use off-the-shelf GPUs (although there are litecoin ASICs now, they don't perform that much better than said GPUs if compared to bitcoin. Mining bitcoin on GPU today is a fool's errand at best). And, more importantly, litecoin is also headed to block halving in August 2019.
With a proven track record, new developments such as new consumer-friendly wallets, cheap payments via Lightning network, and bitcoin interoperability, I consider litecoin to be the single most undervalued cryptocurrency on the market.