The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. -- Werner Heisenberg, 1927
If we will only allow that, as we progress, we remain unsure, we will leave opportunities for alternatives. We will not become enthusiastic for the fact, the knowledge, the absolute truth of the day, but remain always uncertain... In order to make progress, one must leave the door to the unknown ajar. -- Richard Feynman
In A Nutshell: We can never know exactly both the location and the speed of a particle. The more precisely we know one trait, the more uncertain we will be about the other.
Uncertainty Principle - This great video demonstrates it in action.
The Uncertainty Principle - Info from the American Institute of Physics.
Uncertainty Principle - A more in-depth offering from "thebigview.com"
Heisenburg's Uncertainty Principle - Even deeper, with math - for those so inclined…
(While the principle may be about uncertainty, web resources seem fairly predictable in their titles. LOL)
How It Can Apply In Our World
Biological Warfare and the “Buffy Paradigm” - Drawing on a popular TV series, this article discusses how to deal with the many uncertainties presented by biological warfare. (pdf)