As an economic system, Ethereum is very safe and reliable. However, it is quite different from the conventional way of thinking about and managing your finances. The biggest difference is that you have absolute control. This means, that if your wallet is compromised, you will likely lose your ETH, or other tokens, and generally there is no insurance, or central authority to take responsibility. It also has other implications, such as, if you send ETH to the wrong address, you will likely never get it back. This may sound kind of scary... right? To be honest, it is. But it is rather like learning something new. Think about driving a car or riding a bicycle — these are the most dangerous "everyday" activities that one can undertake. However, once you learn how to do it, and act responsibly, it becomes normal.
In short, if anyone obtains your private key, or generating pass-phrase, you may lose all of your wealth. You may already have been a victim of a scam or phishing attack against your conventional bank account. This kind of phishing attack is very common, and applies equally to cryptocurrency. The golden rule is, never reveal your private key or pass-phrase.
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