Focusing on your weaknesses is not necessarily wrong that being said if you have a finite number of hours during the day you want to spend them on what gives you the most benefit. The thing with weaknesses, the more you spend time on them the more stuff you will find that needs fixing. That holds people back from achieving their potential.
Most of us spend most of our life focusing on our weaknesses and that immobilizes us. Coaches that seek to bring true transformation for their clients, and not just quick fixes, have to see their clients as whole and full of potential and hold them true to that potential.