Is the reason why desired matters are not achieved after informing others about them, and everyone admiring what is bought as if it were unique, the evil eye?

The exact cause cannot be ascertained, but the evil eye is real. It is prescribed to guard against it by concealing what might be a cause for it, just as Jacob (peace be upon him) did when he commanded his sons to enter through separate gates, fearing the evil eye upon them. Scholars said that this was out of fear of the evil eye. And in the Hadith: "Seek help for the fulfillment of your needs by keeping them secret, for every possessor of a blessing is envied."

Concealing good qualities is considered a way to ward off the evil eye, just as Uthman (may Allah be pleased with him) did when he saw a beautiful boy and ordered that the mole on his chin (the noonah) be blackened so that the evil eye would not strike him.

It is prescribed to protect oneself from the evil eye by seeking refuge through supplications and Mu'awwidhat (protective surahs), and by using legitimate Ruqyah (incantations).