If a pitcher has the fastest fast ball or the bendiest curveball, but that’s all he can throw he might find some success, for an inning or two here and there. But in the long run they will fail. Hitters will catch up, learn the one trick he has, and crush him. The only exceptions are those pitchers whose one pitch is so good they can use it over and over again (think Mariano Rivera and his cut fastball or Trevor Hoffman and his changeup). But even then they only succeed for three or four outs at a time.
So next time you watch Clayton Kershaw or Felix Hernandez make the opposition look like bat-waving fools, think about this. Find the authors who leave your knees buckled and have you helplessly at their mercy. It’s a good thing to be off balance.