Every Day In Every Way I'm Getting Better And Better - Émile Coué

Émile Coué  who died in  1926) was a French psychologist and pharmacist who introduced a popular method of psychotherapy and self-improvement based on optimistic autosuggestion.
The application of his mantra-like conscious autosuggestion, "Every day, in every way, I'm getting better and better" is called  Coué method.  The Coué method centered on a routine repetition of this particular expression according to a specified ritual -- preferably as much as twenty times a day, and especially at the beginning and at the end of each day. When asked whether or not he thought of himself as healer, Coué often stated that "I have never cured anyone in my life. All I do is show people how they can cure themselves."
Unlike a commonly held belief that a strong conscious will constitutes the best path to success, Coué maintained that curing some of our troubles requires a change in our unconscious thought, which can be achieved only by using our imagination.
Coué noticed that in certain cases he could improve the efficacy of a given medicine by praising its effectiveness to the patient. He realized that those patients to whom he praised the medicine had a noticeable improvement when compared to patients to whom he said nothing. This began Coué’s exploration of the use of hypnosis and the power of the imagination.

His initial method for treating patients relied on hypnosis. He discovered that subjects could not be hypnotized against their will and, more importantly, that the effects of hypnosis waned when the subjects regained consciousness.  He eventually turned to autosuggestion, which he describes as
... an instrument that we possess at birth, and with which we play unconsciously all our life, as a baby plays with its rattle. It is however a dangerous instrument; it can wound or even kill you if you handle it imprudently and unconsciously. It can on the contrary save your life when you know how to employ it consciously.

Coué believed in the effects of medication. But he also believed that our mental state is able to affect and even amplify the action of these medications. By consciously using autosuggestion, he observed that his patients could cure themselves more efficiently by replacing their "thought of illness" with a new "thought of cure". According to Coué, repeating words or images enough times causes the subconscious to absorb them. The cures were the result of using imagination or "positive autosuggestion" to the exclusion of one's own willpower.

Coué  developed a method which relied on the principle that any idea exclusively occupying the mind turns into reality, although only to the extent that the idea is within the realm of possibility. For instance, a person without hands will not be able to make them grow back. However, if a person firmly believes that his or her asthma is disappearing, then this may actually happen, as far as the body is actually able physically to overcome or control the illness. On the other hand, thinking negatively about the illness (ex. "I am not feeling well") will encourage both mind and body to accept this thought. Likewise, when someone cannot remember a name, they will probably not be able to recall it as long as they hold onto this idea (i.e. "I can't remember") in their mind. Coué realised that it is better to focus on and imagine the desired, positive results (i.e. "I feel healthy and energetic" and "I can remember clearly").

Coué's ideas have influenced many writers and even John Lennon  wrote  " Before you go yo sleep say this little prayer  Every day in every way it's getting better and better. "  in his song Beautiful Boy for his son Sean.   Beautiful Boy on Youtube