The world we see has certain unique unchanging features, for instance its dimensionality, the dimensions of the gauge function spaces, the kind of fundamental spin-1/2 particles we have and so on. If there is a simple grand principle which fits all of this and explains most of it, its predictions must be pretty much unique. What has been found so far is that strongly stated principles with unique predictions have failed. Two classes of examples were briefly presented in sec. 3.5. The first is the example of Grand Unified Theory of Georgi and Glashow; it failed because the protons refused to decay. The other example is where uniqueness is not enforced by the principle and then reliance on it becomes suspect. In the case of the Superstring theories, many possibilities exist. During the decade of 1990's a certain economy has been restored, which goes by the name of M-theory. This is indeed a very elegant theory but from the general symmetry requirements of Superstring theory, many other models are not ruled out. Even if we restrict ourselves to the M-theory, explaining the observed world as a consequence of the same is a daunting task. Thus, principles we consider beautiful and simple can also fail to give a unique world.