Not everyone is "good at it" in life. You may think it's you, because of your size but it could also BE Her. Her mind set. Her body. Maybe it's BOTH of you. If you are trying and she is trying, that's all you can do... keep trying. Every part of life is like that. You go to bed. You wake up. And in the morning you decide you're going to keep trying ... at EVERYTHING. You're going to try to shower, so you do. You're going to try to make breakfast, so you do. You're going to try and go to work, so you do. You're going to try to get along with others and do your job well at work, so you do. Even the Argentina soccer team tried to be good... and all the other 100 soccer teams tried to be good at soccer. It's all about trying. Everything is constantly about trying. If your wife stops letting you try .... like for months or something, then you might need to really change. Hopefully you both enjoy trying to be "good" in bed.