I call it the "Prior-Units" theorem. Given that you are able to articulate an idea useful to many people, there exists prior units of that idea. The only way then to come up with a "new idea", is to come up with an idea useful only to yourself (plenty of those) (or small groups), or translate an old idea to a new language.
The reason for this is that if your adult life consists of just a tiny, tiny, tiny fraction of the total time of all adults, and so if an idea is relevant to more people, odds decrease exponentially that no one thought of it before.
There are always new languages though, so a great strategy is to take old ideas and bring them to new languages. I count new high level, non programming languages as new languages as well.
The reason for this is that if your adult life consists of just a tiny, tiny, tiny fraction of the total time of all adults, and so if an idea is relevant to more people, odds decrease exponentially that no one thought of it before.
There are always new languages though, so a great strategy is to take old ideas and bring them to new languages. I count new high level, non programming languages as new languages as well.