We don't think about something unless we were previously interested in it. A person who never took an interest in stamps will never think about the details of stamps, while others wrote entire books about them.
What is the source of interest? Will - רצון. There are two sides to will - negative and positive. A person will sometimes take an interest in something to which he is opposed. I personally think a great deal about abortion. The notion that a woman will willingly terminate the life of her future child really grabs me. I am not interested because I am in favor [unless the women is a member of Hamas, ISIS or any of that chevre - then I would pay for it:-)] but rather because I find it so immoral [barring extenuating circumstances] and unconscionable. I also think about money [too much for my taste] not because I am opposed but because I need it in order to support my family and there is no food or shelter without it. It is my positive interest which created the thoughts.
I never think about how bears manage in the forest. I am not interested and don't care. No interest - no thoughts.
Our job is to get interested in the right things and allow our mind to be there. Our interest should not extend to matters that place our mind in the gutter [who "came out of the closet", which famous person cheated on his wife/girlfriend with which other famous person etc. etc.]
(מכתב מאליהו חלק א עמוד נב)