If someone stole a hide and trimmed it for use, he acquired it, and it is now susceptible to ritual impurity. If he only designated it in his mind as a tray, it also became a utensil susceptible to ritual impurity. But why should it be so, it hasn't changed?

Rav Yosef answered: it is a changed object because of a change in name. It was a hide, and is now a tray. This question remained unresolved for 22 years, until Rav Yosef was promoted to the position of the Head of the Academy and received Divine assistance in resolving questions, so that his reputation would be enhanced.