This paper discusses the most notorious paradox of Special Relativity. The reciprocity of Lorentz transformation applied to a one way scenario is demonstrated on the first leg of the journey, however the only reason of reciprocity is that two systems use two different sets of events resulting naturally from relative simultaneity caused by Lorentz transformation. The actual problem which twin ages less cannot be resolved within the Special Relativity. The relative simultaneity seems to be only an artificial effect of clock synchronisation convention. If it was for real, it would cause violation of causality in some cases, which is demonstrated. There seems to be a possibility that the absolute simultaneity and preferred inertial reference frame are valid concepts, but the Special Relativity still has predictive power without the need of finding them if at all possible.