What's my next pitch?

I've always wondered why baseball pitchers don't just make up their own minds what to throw next.  Why do they need to have the catcher suggest a curve ball or a fast ball?  Doesn't the pitcher know what his best pitches are, how tired he is, and what the batter's weaknesses are?  Why does he need suggestions from his catcher?

I've got a new guess about why the pitcher wants his catcher to call the next pitch and why the quarterback wants the coach to call the next play.  The book "Willpower: Rediscovering the Greatest Human Strength" describes how we each have limited willpower.  It fatigues from uninterrupted exertion.  A baseball pitcher needs to push himself to extreme levels to throw 100 pitches in a game at speeds often exceeding 90 miles per hour and to do so with accuracy, variety, and deception.  Every pitch is draining.  And decisions about what to pitch to throw next are also draining.  I suspect that all baseball teams learned over time to take some of the burden off the pitcher.  You can't spare him the strain of throwing the ball.  But you can let someone else decide what to throw next.