The world of contracts is really interesting. Imagine a country Byteland that has a problem with alcoholism. Lots of people get too drunk and bother others. The parliament gathers and decides to issue a new law. First they try "it is illegal to bother other citizens in public" but the problem is, how do you legally define "to bother other citizens"? Then someone has a bright idea - make a law "it is illegal to be drunk in public". The idea is, only those who are annoying fucks will ever be checked, for obvious practical reasons. Everyone happy, the law passes. Citizens enjoy their beer, but they know that it they drink too much and start causing problems, they'll be arrested. One day a Sillycoin Valley startup comes up with great technology - a device that can pinpoint who exactly is drunk within two kilometers of range. Now suddenly lots of citizens who had just one beer and are minding their own business start getting fines.

The point I'm making is, there is a difference between what contract explicitly says, and what is implicitly understood due to practical limitations of the real world we live in. When the real world changes so does the effective implementation of contracts, even though the contracts themselves don't change. The problem is, by the time the world has changed against your favor, you might not have the power to demand an adjustment to the already signed contract.