Never Lose Something You Won't be Able to Ever Find Again

If I ever find something of worth, like a seashell, do I let it be lost under the ocean floor or do I put it in my pocket to save and keep?
The most unique shells are not like the others. It catches your eyes; there is something about it that makes you want to pick it up. Perhaps the ridges, the color or the shape. Usually it is the slightly broken ones that grab your attention. I know that i'll never find another one like it....I may hold onto it for awhile as I roam the beach but in the end I throw it back out towards the ocean only to get swept back to the tide where someone else will find it. Or it will go farther out sea to perhaps never be found again.
The next morning I come back to where the masses of shells lay. I changed my mind. I've thought of nothing else but to find the shell i've once dropped. No matter how hard I search I can't find THAT shell nor one that looks anything like it. I lost it.
Was it a mistake or will I find an even better shell the next trip I take?