A little while ago I was thinking about why women love fat diamond rings so much. They are not in any way functional as they have no real use. They're not especially rare if not for the limited supply organized by the diamond cartels. But they love them. The bigger the better.

Then I thought about what actually happens when you buy a woman a diamond ring.
You, a man, spend a very large amount of money on a useless shiny piece of carbon and give that to the woman you are marrying.
You take your useful resources (money) and spend a large amount on something that is completely useless and you give it to this woman to wear on her finger.
Women love this because it's a huge show of commitment. It's a show of how much resources she was able to extract from you.

Now she can nonchalantly wear this act of commitment on her finger for the whole world (especially her friends) to see. She can subtly show off how she managed to snag a high value man and got him to commit to her so strongly that he would sacrifice huge amounts of money on a shiny rock for her finger.

Sorry if this is inappropriate for this sub.

Edit: was not expecting such an amazing response. Full of quality replies. This sub is awesome.