In short, there is a mystery person named Satoshi Nakamoto who created the white paper on Bitcoin (https://bitcoin.org/bitcoin.pdf). This developer's concept was to create a peer to peer electronic cash system which did not involve a third party. The dilemma is that third parties, such as banks and credit\loan lenders would get in the way and tack on fees to people wanting to send money to others. It's like if someone wanted to send you money through Western Union, they would have to pay a fee to do so.
Nakamoto's aim was to minimize the involvement of third parties. He devised a de-centralized blockchain validation system which uses computers to account and validate units of value. Now, this system has a limited quantity of around 21 million of these units, and each unit can be subdivided into smaller portions. To paraphrase, Nakamoto created a system that can validate an accountable unit which does not need a government or bank to verify who owns what, and if it actually exists.
In the beginning, people used this to purchase items anonymously. Early adopters were people trying to buy drugs. People started putting money into the system, thus giving each unit a value.
People started noting that with this new Bitcoin unit, banks could not cease it from them. They also noted that the more people invested, the more value they would gain just by holding the units. The fees for paying something with bitcoin is cheaper than using a credit card for the retailer.
Fast forward to now, crypto currencies are an option to hold monetary value outside of a bank or government. This is really good for places like Greece where the government and banks have ceased the assets of people before. With crypto currencies, that is not possible. Somone's fortune can only be calculated if they give out something called a private key, which is generally their bank account. From the private key, public keys can be generated which are portals where they can take in crypto currency.
The value is in absolute control of your money. Since more people are getting in, each unit is getting more valuable. This actual public world trust of value is working out to be a viable option. If Bitcoin can get 0.001% of the worlds value, it is estimated to boom.
No government or bank would be able to take it from you as they can right now. It's basically a Swiss Bank Account, but with growing value since all values are spread out evenly to each unit.
With they way it is rising, we will regret that we didn't invest in Bitcoin when it was under $25k a coin. in two years, what ever is invest now will be 1/5 of what will be there in 2020. The only way of shorting it would be if another crypto takes precedent or people find a better way to gain interest on their investment.
TLDR; Bitcoin is undervalued. More people and businesses will invest into it over time. It doesn't matter if you believe in it or not, because the investors are pumping it up and holding their bitcoin.