That's because of the curse on Marvolo Gaunt's ring. Anyone who tried to wear the ring will be cursed. He wanted to revive a dead family member and forgot that the ring is a Horcrux. It nearly killed him but he asked for Snape's help to counteract the curse.
Quote:
Snape: "Why, why did you put on that ring? It carries a curse, surely you realised that. Why even touch it?"
Dumbledore: "I... was a fool. Sorely tempted..."
— Dumbledore explaining why he would adorn the obviously cursed ring
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