tusenfem showed graphically a wonderful example of the concept of the uncertainty principle.
in a nut shell, when an observer like yourself is trying to find and measure a particle, say for instance an electron in a region of space, you will find that the electron is moving, and the more precise you try to measure the "momentum" of the electron, you find that the position of the electron is uncertain.
but why does this happen?
from what i understand, and i may be wrong, but when you try to look at a particle (say an atom), you need a way to observe that particle so you would need to use a photon to observe or see it by looking at the reflected photon. However, when the photon entangled the particle, it changed the momentum/position of the particle by an uncertain amount which would be inversely proportional to the [accuracy] of the position measurement.
http://en.wikipedia.org/wiki/Uncertainty_principle