There are very few places in law where you can legally stake a claim within someone else's territory and exploit it for profit. Our patent system is one of them

There are very few places in law where you can legally stake a claim within someone else's territory and exploit it for profit. Our patent system is one of them because it allows one inventor to patent an improvement to another inventor's patented invention. That should (1) encourage early inventors to continue to invest in improving their inventions before someone else does and (2) encourage new inventors to improve on existing, still-patented inventions by giving them ways to profit from their improvements.