Originally Posted by gmatheis
When your effort is all on hitting the ball back you often give a larger margin of error because you aren't concentrating on exactly where the ball lands. This is why people will often play a ball that is out by an inch or two when they are trying to hit the ball still.
On the other hand when you have given up on hitting the ball and just watch to see if it lands in or out you can be more precise as all your concentration is focused on just seeing if the ball landed in or out.
SO be grateful that you have been getting some "benefit of the doubt" calls when your ball is only an inch out, rather than being angry when they actually call it.
When I am returning serve or am trying to set up for a deep rally shot, I'm concentrating on making the shot, looking to see where my opponent is moving, etc. So usually I get only a brief look at where the ball actually lands. Under that circumstance I end up playing a lot of out balls because I don't want to make an out call unless I'm sure.
On the other hand, if I'm just watching to see where the ball lands, but nothing else, I can get a much better look at it, and can make my calls with more confidence.