What is likely to happen if every morning a person low in self esteem repeats self affirmations such as "every day, in every way, i am getting better and better"?

Slowly but surely their self esteem will improve because it takes that self assuring voice for someone to start believing in themselves so there is a high probability of the person to start believing in themselves or to start being confident.

There is a saying which says if you think you can, you can but if you think you can't, you can't.

So as the person keeps saying he is getting better the mind may start to believe this and it will become their reality with time.