I believe.

Mental strength is crucial for a happy and successful life. It means that a person can manage his emotions and thoughts despite of the circumstances. It also means to be strong enough to reach your goals and live according to your own values. The details I think are important here :
An Affirmation is a thought about yourself or anything else that is having more of an impact on you than you realize.
It said that whenever you think, hear, or say things with “I am” or “I can” or “I will” you are making a self-fulfilling prophecy. Whenever you say anything of this nature you are unconsciously working to fulfill that goal. So it is important to mind what you think of yourself. I wanted to believe what it said, that just by changing my thoughts I could change my world I cried because it was such a big thing to me and I wanted to hold to it dearly and believe it sooo much that I gave it a try as best I could.
From that moment on I told myself “From now on whenever I think a thought that is negative about myself  I will replace it with I am happy , I can be happy, and I will be happy much sooner than I think I will.” Whenever I thought about something bad about myself I forced the other thought in and thought only about that until I felt that the old feeling and thought had been replaced. I had to do it over and over again but to me this was life or death important. One thing that’s important to remember is your feelings. If your thoughts aren’t in the right place, if you feel negative emotion, even if you think the thoughts you want, you are in ALL cases attracting that which you do not want and NOT getting what you do want, it is that simple.
So what’s the key? You must BELIEVE what your saying to yourself, or else the positive words and thoughts you are thinking are just hollow words, and nothing more. Look into the mirror and find reasons to love yourself, and don’t just find them Love them! Actually Love yourself, feel that love and know that all is well and your there. Love your body because you have it – you don’t have to work out, just look in the mirror and love you for you, where you are at that moment in time and the deed is done!