The Propinquity Effect
how: an enzyme is able to effectively make a reaction intramolecular by binding the reactants in the correct conformation in close proximity within the active site this can speed up the rate of a reaction dramatically, intramolecular rates avoid diffusion control and have prearranged conformations which is far more efficient than typical intermolecular reactions,
why: enzymes are outrageous, evolution has pushed them, through trial and error, towards optimal configurations that, almost magically, provide ideal conditions for a reaction to occur