Frequently rediscovered technologies

Greenspun's tenth rule of programming says

Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.

Here I'm going to take seriously a rule that was only not entirely serious. It's saying three things about Lisp.

1. It's a frequently rediscovered technology. There's something inevitable about it.
2. It's not completely widely known. Not everyone knows about it, so they don't know that they're reinventing it.
3. It's not easy to implement, hence all the poor implementations.

The same could be said of state machines. A number of projects have grown until they contained an ad hoc, informally-specified, bug-ridden, slow implementation of state machines.

What are other ideas like Lisp and state machines that are frequently and poorly reinvented?