"Nurture you mind with great thoughts". A quote from Icelandic welterweight star in the UFC, Gunnar Nelson. Doing the act of nurturing your mind with great thoughts can be likened to planting seeds; it's the seeds which are planted which allow the growth of the beautiful flowers, vegetation, and trees. The planting these great thoughts will manifest in the future, as you long as you continue to water them, so to speak: as long as you continue to repeat them in your mind.
It's about programming the subconscious mind. It is believed that 90 to 95% of the time we are operating on the software of our subconscious mind; so if we can program that mind to believe the things that we want it to believe, then the results can be astounding. One of the ways to do this is via affirmations, and really feeling the feelings associated with the affirmations and getting into these affirmations as much as possible. Having that ultra realistic feeling of sensing all the senses in the affirmations, visualizing them, and generating the emotions associated with them, amplifies their impact.
Rashad Evans, who holds a degree in Psychology, feels the power of affirmations can be strong. In the video at the bottom of this post, around 5:40 into it; he explains that he was able to gain a stronger conviction in himself and belief in his abilities via the nurturing of great thoughts in his mind:
"I am the best"
"I won't be beat"
"I can't be beat"
"No one can beat me"
These mantras are just words but after a while it becomes a conviction in my soul.
The last line is a key component to all this: after a while it's a deep conviction. No longer is it work to try and force these beliefs onto yourself; but rather it's just a fact. Just like when you slip a switch you know the light comes on, or when you turn a faucet you know the water will drip; you just know and accept these great thoughts as facts. All of a sudden it's a just a natural thing to think that you are great and can do great things.
The sky blue, the sun is hot, I am great.
It's just something that is part of our reality and requires no thinking at this point. That's when the subconscious mind just accepts this and you operate from that position 90 to 95% of the time without even thinking.