  The Born's rule introduces intrinsic randomness to the outcomes of a
measurement performed on a quantum mechanical system. But, if the system is
prepared in the eigenstate of an observable then the measurement outcome of
that observable is completely predictable and hence there is no intrinsic
randomness. On the other hand, if two incompatible observables are measured
(either sequentially on a particle or simultaneously on two identical copies of
the particle) then uncertainty principle guarantees intrinsic randomness in the
subsequent outcomes independent of the preparation state of the system. In this
article we show that this is true not only in quantum mechanics but for any
no-signaling probabilistic theory. Also the minimum amount of intrinsic
randomness that can be guaranteed for arbitrarily prepared state of the system
is quantified by the amount of (un)certainty.
