Having a walnut tree in your yard is a very mixed blessing. If you don't pick up the nuts, they decompose on the ground and drastically alter the chemistry of your soil. While grass will grow under a walnut tree, some flowers and shrubs will not thrive nearby. There's also that annoying clanking noise you hear when you run the mower past your walnut tree. It's true that a prolific walnut tree will keep you in nuts for free, but taking advantage of this bounty requires some work.
Walnuts have an extremely hard shell, which often shatters when broken.
To complicate matters, the dark nut meat is often indistinguishable from small pieces of shell and you invariably get a few small pieces of shell mixed in with the meat. Dentists love this about walnuts. True walnut enthusiasts have shellers, which smash the shells in a vise-like apparatus and allow you to separate the meat from the shells in fairly short order. However, this requires an investment that may not appeal to someone who just wants a couple cups of walnuts for turkey stuffing or holiday bread. For the occasional walnut sheller, whose technology is inspired by the Flintstones, the tool of choice is a medium-weight hammer.