According to D. P. M. Mingos, in his book Essential Trends in Inorganic Chemistry, the bond order of the three-centre four-electron bond is approximately 0.717, which is one divided by the square root of 2. However, in the case of the three-centre two-electron bond, the bond order is 0.5. This would imply that the former is stronger than the latter. However, both of them have similar-looking molecular orbital diagrams. In the case of the former, the nonbonding MO is filled while in the case of the latter, only the bonding MO is filled. Thus, from the MO perspective, why would these two bonds have different bond orders?