is it possible to LOSE all the MONEY INVESTED in a cryptocurrency?

Yup:

1. if all the people stop being interested in a cryptomoneta you have, the network could die because there would be no more people running the full node clients and the minerals on their devices for that coin. In this case, the value is reset because the coin is actually dead. It can happen with little-known currencies, just born;
2. the technology on which the cryptomonete is based is a "secure for design" technology, that is inviolable, but to make it happen we use cryptographic and hashing algorithms whose security could be violated. If someone succeeds, and makes it known, the currency loses instantaneously in value because any person in the world could carry out transactions on behalf of any other person and therefore makes no sense;
3. if you keep money on an online wallet (like Coinbase) a hacker could be able to break your account and steal them or, worse, could be able to violate the online wallet servers you have entrusted to and steal the money of all account holders. It happened a month ago in NiceHash;
4. always if you keep money on an online wallet, this could fail for any reason and do not have the money to pay depositors. As happened years ago in Mt.Gox;
5. again, if you keep money on an online wallet, the creators of that service could one day disappear into thin air with your money (it was a scam service);
6. if instead you keep the money on your PC (which you can do by running the full node clients), the security of your wallet depends on you and not on third parties. But you have to be careful: if you lose the wallet file, the money after that is irrecoverable;
7. the currency in which you have invested is then revealed to be a scam currency or a ponzi scheme (fraud);

Currencies (including cryptocurrencies) are securities. As such they are subject to the laws of the market. Their value can go down or grow over time. Tomorrow the Bitcoin can be worth 1 cent the piece as well as 1 million euro piece. Investment is a gamble - the one in cryptocurrencies is a high risk and high return investment: you can earn a lot, but also lose a lot. Anyhow:

• it is advisable to avoid entering into a high-risk investment without having adequately informed about how cryptocurrencies work (also at the technical-IT level) and the financial and forex markets. Without a basis of financial and computer science it is not an investment: it is an attempted suicide;
• it is good to invest only what you are willing to lose and not a penny more;
• one must evaluate whether to simply make an investment (that is to deposit money in cryptomonete and return after months or years to collect them) or whether to trade in the short term (in which case one must stay behind every day, but the earnings may be higher). In the first case, it should be informed about economics and finance, since in the long term the main factors that drive prices are fundamental factors of the economy; in the second case, he should learn to analyze graphs and indices. Moreover, in the first case it is generally preferable to keep money in a wallet on your PC, without depending on third parties; in the second case it is necessary to keep the money online in order to exchange them quickly;
• it is important to keep constantly informed about market trends, especially the forex market.