Quantum mechanics describes everything with "wavefunctions" or "state vectors" that provide probabilities for position, velocity, etc. As Caraiani Claudiu says, the mathematical details make it impossible for a wavefunction to provide a probability of 100% for a particular position and a particular velocity.
Also, it has been proved in many ways that it is very difficult to make a deeper theory that explains quantum mechanics - to propose a new set of laws which give rise to an average behavior that matches quantum mechanics. The theory of David Bohm is the simplest approach to this, but it is hard to extend it to relativity and to fermions.
So most physicists attempt to believe that quantum mechanics is the final framework of physics, and they construct rationalizations for this intellectual position. They will say that nothing is real until you measure it, or that the electron does everything at once until you look at it (and then you see it doing just one thing), or that by definition we don't see what we don't see so we shouldn't care if the theory offers no coherent account of what happens between measurements.
Among the attempts to make sense of quantum mechanics, I should also reserve a special mention for the belief in "many worlds", according to which all the possibilities in the wavefunction are equally real and happening in separate parts of a "multiverse". At least this looks like an attempt to restore an objective conception of reality, without verbal games. However, if you examine the details, you will find that there is no "many worlds theory" in the sense of a coherent, self-sufficient set of concepts. Possibly there could be a many-worlds theory one day, but at the moment it is just another wall of words.
There are several reasons for the persistence of this pathological situation.
First, quantum mechanics works very well. It doesn't just make successful predictions, it is a framework which can be extended to include new particles and new types of interaction, without abandoning the uncertainty principle and all the other features which make it unsatisfactory as an ultimate theory.
Second, although it does not offer a conceptually coherent account of objective reality, it does offer a coherent self-contained framework for making predictions about observable phenomena, if that is all you are interested in.
Third, the mathematical difficulty of fundamental physics is such that people have no room in their heads for also trying to explain quantum mechanics itself. The people trying to do that, with very few exceptions, are usually not working on the most advanced theories.
And fourth, it must just be difficult to discover the truth about this. We may have to develop some entirely new set of concepts by means of which to understand basic entities and their properties. There may be no particles, and there may be no position or velocity as presently imagined. Those may simply be informal common-sense concepts, pushed into domains where they don't actually apply. Whenever you hear someone saying, quantum mechanics definitely implies some particular picture of objective reality (or even worse, saying that it implies that there is no objective reality), you aren't hearing truth, you're just hearing dogma, the desire of a human being to be in possession of the truth even when they aren't.