possibilities are real just because they're not impossible

From the world that acutally exists, it is quite clear that the world and all its detail is, at least, possible. Hence, whatever exists now must have been possible at all times in the past (otherwise it could not be here). This is an argument from metaphysical necessity--but it seems to work. That is, it establishes fundamental notion that possibilities are (by their very nature) not impossible and could, therefore, attain actual existence at some time. Simple put, whatever exists now must be possible. The corollary to this argument is that possibiliites could never have been stricly impossibile. For, in that case, they could never have appeared.
This series of thoughts is bolstered by the quantum mechanical requirement that an object is the sum of its total possibilities.