In light of the recent 10-dimensional superstring and 11-dimensional M-theory, what is the true meaning of spacetime need to be clearly defined as what mathematics exactly can do. When the mathematics becomes vague and ambiguous then its use loses its logical power of communication and ceases to be assertive and informative. Compounded by its empirical unpredictability, it becomes useless and meaningless. The question why physical reality only appears as 4-dimensional, 3 of space and 1 of time, must be emphatically answered. Special and general theory of relativity are both based on 4 dimensions. They were and still are successful in theory and practice. Quantum mechanics, due to its probabilistic nature cannot truly be more than 3 dimensions (2 of space and 1 of time). There seems to be a relationship between probability and dimension. Even dimensionality are by nature contains more uncertainty and probability than all odd dimensionality. This is the reason why M-theory 11-ness is more predictive than the 10-ness of superstring. 3-space dimension is more predictive than 2-space dimension. 1-time dimension is more predictive than 2-space dimension. 3-space is more predictive than 4-dim spacetime.