Nothing is certain. Sure, you have heard that before, when contemplating the unpredictable nature of human existence. However, the Heisenberg's uncertainty principle deals with something equally useful as a workout for our imaginative mind, but can actually be proved. Or it can not, whatever you think success in this case is.
Subatomic Is Tough!
In 1927, Werner Heisenberg, a renowned physicist from Germany, suggested how it is impossible to know both velocity and the position of a particular object. For Heisenberg, this was also impossible on a theoretical level, let alone in a real situation of taking measures. This principle that is also known as the indeterminacy principle, is probably the most critical postulate of quantum mechanics.
The Heisenberg principle is used when we talk about really small objects, meaning atoms and subatomic particles. When we measure the speed and the position of a plane, we are dealing with a large enough object, and the problems that come with measurement come only when we observe objects that are too small, and hence difficult to observe accurately. Only in those scenarios, the result that we get can be, strictly speaking - wrong, or when we put it back into perspective - uncertain.
All of this has nothing to do with the way the speed and position are being measured but is a result of subatomic behavior. The connection between particles and waves is a close one, and any attempt to, let's say, measure the movement of something small as an electron, sways the process in an unpredictable direction.
Wave-Like Particle Behavior
Particles, in a way, behave like waves. Waves are, and this is your non-quantum-mechanics inspired type of guess, something that moves. Technically, it is the act of freezing the particle that moves like a wave, that creates the situation of uncertainty. If you "stop" a wave, you can no longer determine the overall wavelength, which means you know the position of a particle, but can not be sure what velocity it has.
So, simply speaking, the Heisenberg's uncertainty principle, always insists how a precise measurement of one particle feature (position), makes it uncertain to claim we got it right with another feature (speed).
As a consequence, we can look at Heisenberg's uncertainty principle as something that is fundamental - a theory that can be applied to all forms of matter or energy. That is where quantum mechanics comes into play.
Quantum mechanics is a very specific field, as it tends to offer explanations of the physical world around us in a universal way so that the rationale of the theory applies to everything. The Heisenberg uncertainty principle is what makes quantum mechanics different from other approaches. In the very core of quantum mechanics lies the notion of how more precise measuring of velocity, or momentum of a particle, leads to less precision when it comes to determining the position of that same particle.
This kind of epistemological cut is what makes explanations offered by quantum mechanics so revolutionary. The importance of quantum mechanics, with Heisenberg's uncertainty principle as a fundamental idea driving the answers about the world around and beyond us, is immense.