In the book ‘How To Meditate’ Kathleen McDonald (ISBN 0861713419) defines meditation in this way (pg.6):
The Tibetan term for meditation, gom, means, literally, “to become familiar”. What arises in our mind is what we are most familiar with.
This quote refers to the knee-jerk reaction that we immediately go to when faced with difficulties. Do you straight to resentment or disgust? Kathleen McDonald is saying that we go to that reaction due to familiarity or habit. That is what we have done in the past and that is what we will continue to do in the future. But Kathleen McDonald is also saying that by changing our habits then our reaction can be different. We gain this familiarity and habit through meditation.
One high lama described how we already meditate all day, we just meditate on the wrong thing. We meditate on how the person at work speaks badly to us and how irritated we feel. We meditate on the situation at home and how angry we feel. In the book ‘How To Meditate’ Kathleen McDonald describes how to meditate on something more positive that can bring about a positive change in our reactions to difficulties.