system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are land/real estate lease agreements often for 99 years?

Everything from Hong Kong, Daewoo in Madagascar, to housing in Singapore. Why exactly 99?
gpt
In much of the English speaking world, or at least parts of the world where the judicial system has some connection to merry olde England, an old legal doctrine called the Rule Against Perpetuites was part of common law.  There is no way to properly ELI5 the RAP other than to say it was designed to stop the "dead hand" from controlling property more than a generation or so after the original owner died.  In order to conform to the RAP, a 99 year lease was developed, and in most cases, it was deemed not to violate the RAP.  In modern times, the RAP is more or less defunct, but the tradition of a 99 year lease was established and continues mostly due to practice and convention.