Stand guard at the door of your mind.
The best advice I ever came across on the subject of concentration is: Wherever you are, be there.
There is something magical about putting a problem in writing. It is almost as though by writing about what is wrong, you start to discover new ways of making it right.
Purpose is stronger than object.
The most valuable form of discipline is the one that you impose upon yourself.
Direction determines destination. So the question you must ask yourself; 'Are all the disciplines that I'm currently engaged in taking me where I want to go?'