Why am I always the bad guy?

My wife and I don't fight often, but whenever we do, no matter who was wrong or right, I always end up being the one to apologize. Usually not a problem, as I just want the fight to end and for both of us to move on. But I'm starting to get tired of it. Neither of us are perfect, but it seems difficult for her to accept that sometimes she is the problem and it's not always me. I can't have this conversation without her getting upset; finally just tried to and she's locked herself in our room. How would you recommend I approach this with her? I can't just keep taking the blame all the time anymore.