Our weaknesses and our failures are our greatest teachers. As a human being, I want to be liked and absolutely never want anyone to hate me. However as a teacher, it is my job to point out the weak points in the student's technique and this can yield a strong response. The more experienced you become or proficient you become yields more (for lack of a better word) criticism. Pointing out the shortcomings usually comes at a risk because the criticism usually comes up against the ego. For me, I think that if I point out something that the student may or may not be aware of then they can work towards fixing it. Sometimes to the student, they feel like I am picking on them or accidentally take it personally.
In the martial arts there is actually no victory or defeat nor is there right or wrong or good or bad. There is only a lesson to be learned. Every time something happens to me welcome or unwelcome, I try and see the bigger picture and how this lesson fits into my life. I know that if I can be willing and open to the lesson then I can learn and eventually become better.
There is a description of a scroll in Tea Life, Tea Mind that reads: Be rebuked, Stand corrected and learn
I find this to be incredibly true. Don't take it personal, but take action to personally overcome your weaknesses. This is the crux of martial arts training. The only true defeat is in giving up.
A slip is not a slip but a chance to get to know the floor a little better. All it takes is a change in your perspective.