Oh yes, it is true. I'm not trying to make you overconfident or something and I'm telling you this based on my own experience.
Why do we make affirmations? Someone else can also tell us, "I'm confident", "I'm good in my studies". Right?
You guys see I have a habit of talking to myself. So basically, my best friend is me, myself. So, whenever I make affirmations, I see a positive change in myself and when I compliment myself or am very satisfied with myself, the one who is the happiest in the room is me. But when I am disappointed and say words like "You're a loser"," You don't deserve to have something good in your life", it makes me feel the worst. Even worse than what I feel when people mock me about my "problems".
No one can make you suffer, only we make ourselves suffer.
So, to make yourself study better, you have to say to yourself words such as, "I'll do better", "I'm hardworking", "I'm good at studies", etc. No need to exaggerate things. Why? Because it will sound too unbelievable which won't give you better results.
Don't upset yourself by saying the wrong words. Saying words like, "I'll never do better", "I'll be alone forever", "I'm sure I'm never going to score well" will make your morale down. It might even make you go all depressed. Which is not a great thing to do.
Even when you feel upset, don't say such things to yourself. Instead, Write down whatever you feel on paper. Write about why are you feeling sad, Who disappointed you the most, How you wish things turned out to be, etc. When you start writing or even typing, the solution itself will come into your mind, and trust me, that would be the best advice you can ever get.
Your mind will work better.
This will also make you feel independent. You don't have to rely on someone, You won't need any sympathy from people. I know, that sometimes for stuff like feeling upset and all, it's best to talk to your friends or family but many times, they can't understand our perspective.
And you can't expect it from someone.
You cannot expect that everyone will understand your way of seeing things and that too, every time. So, you can't speak all that out and think about getting sympathy. If you have no one, just talk to yourself. Console yourself.
Tell yourself that you're not weak. You can do anything.
I believe there is not much to say here.
You have to believe that you can do good. If you don't have confidence in yourself no one else will have it in you either.