Suppose that the bike is comfortable on your typical ride. Then, on a lark, you tweek this a bit and then tweek that and find it is even more comfortable. Does this mean the first fit was wrong or does it mean that a comfortable fit occupies a spectrum of possibilities. As most of us with a few several years worth of miles under our belts, best fit is a moving target that changes with physical fitness.
Best fit can change for other reasons also such as a racing fit or a touring fit and the list goes on.