The uncertainty principle was published by Werner Heisenberg in 1927 and is based on the fact that the light needed to observe a subatomic particle will disturb it making measurements uncertain though it goes beyond that. Planck's constant is too small for the uncertainty principle to show up in the macroscopic world but it is significant in the subatomic world.
So the more accurately you measures a particle's position the less accurately that you can measure its momentum and vice versa. This is not the case just because the act of measurement disturbs the system; which it only does sometimes; it is related to Wave-particle duality. The same applies to other quantities as well such as energy and time.
A recent development in the debate between determinism and freewill is the idea that the uncertainty principle is a possible avenue for allowing for freewill in neurology. This based on evidence of quantum, mechanical processes like tunneling being involved in synapse activity.
The uncertainty principle shows that that there are limits to our ability to make measurements of the subatomic world. It shows that there are limits to our possible knowledge about the universe.