I believe what he is trying to say, and my apologies if I am being presumptuous, is that by telling somebody what is going to happen in their future; distant or near, and no matter how accurate or inaccurate you are, will affect their choices and snow- ball into affecting larger events and chunks of their life.
By telling somebody that they will red shoes tomorrow, you have removed their choice in the matter and make in much more likely that they will wear red shoes, regardless of whether or not that was their original intention. You can apply this example to almost any future prediction scenario.
While I am not attacking others abilities, as I have witnessed myself great accuracy and talent in the field, I will certainly say that knowledge of the future, or knowledge of predictions, can be more harm than help, and in a round about way, steals away individual choice, and human mystery.
I suppose this is ironic coming from someone who practices Tarot!