Fitt's created an equation for location (proximity, really) and size of UI elements and their relationship to how easy they are to select. Sometimes buttons should not be easy to select (a great example is provided in this video for industrial equipment).
I't's a classic example of science in user experience and one that is dear to my heart.
Is it obvious? It's certainly logical....but test your skills by attempting to answer the instructors question correctly at 1:50. If you got it right, awesome!