' .... a man sooner or later discovers that he is the master-gardener of his soul, the director of his life ..'
Mind of a man is like a garden and there is no 'Neutral Land'.
If you take care of a land, put some good seeds, take out the unwanted weeds etc. then it will be developed in a good Garden. Otherwise there will be wild growth and only weeds will grow.
Similarly if you do not take care of your thoughts, then your will be also have all types of wild thoughts and corresponding circumstances.
In a man's mind all types of thoughts comes and goes out with lightning speed. It is responsibility of the individual to retain the Good once.