When using the staples I found a pair of pliers to be very handy. It allowed me to put more pressure on the staple to get it all the way in.

reasons, it looks like the tool is all the way in which is good. I had some troubles with the tool myself and went straight to the staple. I then used the same staple for the rest of the psu. I think the staple is slightly thicker than the tool pins which will put more pressure on each side the the pin tabs. Even when pulling the cable out I felt a little pop. Don't give up, the benefits will be worth it.