Dreams are the traction of the desires of your heart. What you dream are the things that you mind has been thinking of. A dream is not controllable because it is an unnoticed desire of your heart and mind.

Oftentimes our dreams served as our motivation in life. We are driven by the desires of our heart and live with it. So it is the dream that controls us. It is what we live. 

I dreamt of becoming an Engineer and that dream controls me of what I do. It is simple that dreams are directions of our desires.