I Planned To Make A Private Key Out Of String (So You Can Remember It Easily)(This Maybe A Dumb Idea)b
Actually, this is a (very) bad idea.
Wallets (containing private keys) created this way are called 'brain wallets'.
The reason this idea is bad, is because the human brain can only 'create' a very small amount of entropy.
Even if you believe your text phrase is completely random, it will in fact be WAY less random than a computer could produce it.
A human brain is said to be able to produce about 20 - 30 bits of entropy. Thats extremely low in comparison to 256 bits of entropy.
Using sentences or phrases from a book is an even worse idea. Cracking brainwallets is doable and can be quite profitable.
Cracking randomly generated private keys on the other hand, is not possible.