What is Social Engineering?

Social Engineering is a kind of fraud. When people try to get money in this way, they usually pretend to be a person who is close to the objects.
For example, in Japan, recently there are the people who try to get money in this way which is called "OreOre fraud". Their target is old people because they have much money and are cheated easily.
Fraud pretend to be a son or daughter of old people and tell a lie to cheat them. The lie is like this, "I'm in trouble and I really need money to solve this problem, so please pay the money into my account."
The important thing is that don't say the name, just say "I" to cheat and if old people ask them "Does your voice changed?", just say "I catch a cold."
I don't understand why the old people were cheated in this way, but clearly, many old people were cheated and taken their money.
Now, this type fraud is unusual because this way is well known, so we can easily recognized. However, fraud created new way. They changed a person to pretend. They pretend to be a policeman or a fireman and this way becomes mainstream. We can find out whether they are fraud or not if we pay attention it.
What will happen if we completely protect our money from fraud? Do they disappear? well, I don't think so, I think they will create new ways and we will try to protect ourselves and it will continue like vicious circle.