From: Power of Positivity at http://www.powerofpositivity.com/3-mantras-help-regain-self-confidence/

3 Mantras to Help You Regain Self-Confidence:

1) “My time is too valuable to waste it worrying about the things I have no control over.”
This mantra came about because, obviously, because I was having obsessive thoughts about things I had no control over. Worrying about these things wasn’t going to change the outcome. All it was doing was robbing me of my sanity and peace of mind in the moment. As soon as I decided that my time was valuable and needed to be respected and used in a more productive way, my thoughts changed and this mantra came into my mind.
Every time I started stressing out, worrying and thinking about scenarios that I had no control over, I would repeat this mantra and almost instantly my peace of mind would start to creep back in and I was able to once again enjoy being alive.

2) “The outer is always a reflection of the inner.”
This is a great Buddhist philosophy and the more I welcome it into my life, the more apparent its truth becomes to me. Whatever is going on around you, whatever you are feeling, whichever situations are angering you or pleasing you, is a reflection of what is going on inside of you. It is not a reflection of the innate state or meaning of that situation. It is a reflection of you. If you are feeling neglected by a friend or a lover, you are probably neglecting yourself. If you are feeling loved by life and the things in your life, you are probably being loving yourself.
Nothing has a particular meaning to you until you decide it does. You could be lacking money and choose to feel sorry for yourself or choose to be grateful for the fact that you are alive and have abundance in other forms. It is not situations that dictate how you feel. It is YOU who dictates how you feel. Every time a situation in my life starts to feel crappy to me, every time I start arguing with someone or feeling rejected by something, I try to remember this and instead of reacting to the situation, I try to explore what it is inside of me that is causing the bad feelings.
After I have done this, I can usually come to a place where I can respond in a way that is productive instead of creating more conflict in my life. It is an incredibly beautiful and empowering thing.

3) “I take nothing personally.”
I would bet that you, like most of us, take a lot of what other people do to you personally. I found that a lot of my peace of mind and confidence was being robbed by the fact that I thought other people’s feelings towards me were a reflection of my own inadequacies. But then something occurred to me: No one on this earth can see further than their own mind. Everything anyone else is doing or feeling in relation to you, whether that means someone is offended by you, rude to you or loving to you, is a reflection of how they are feeling on the inside, but they are not saying something about you.
No matter how perfect you are or how great of a person you are choosing to be, someone is always going to have something crappy to say about you. Now does that mean that you should fully disregard the opinions of every other person on this planet? No. But it does mean that you can understand that most things in life are just that- opinions. They are not right or wrong. They are just a reflection of where someone is at in their life and that doesn’t have to define you in any way. You define you. No one else.