That's a valid sentiment, however we can define reasonable expectations in this case, set based on measurements like arm length. In this case, being able to focus on items held in the hand might be the benchmark. Being able to focus on items a millimetre or less from your eye would not be useful since humans (on average ) do not have the motor skills required to consistently place and hold such an item.

Just like a person can be both average weight (in a group of other people) and overweight (from a human health point of view).