If someone sent a link by mail or message , what is wrong in clicking on it and checking what it is ?

Well, you are exactly the kind of a person who are targeted by cyber criminals. In most of the cyber crimes, it is the phycology the users that are primary targets than the technology itself. From swindling small amounts from you savings to completely lock your data or encrypt your data (Ransomware ) could be the result. This may also lead you to be blackmailed. They may come up with messages or calls stating that they have recorded your personal activities by taking control of your camera. Or they may say that they have your personal data stored in your gadgets which they will publish or transmit. Or they may just ask you to pay for returning your data.

So the important thing to remember is – “BE CAREFUL”.