The difference between being aware of the thought and thinking the thought is very real. But it is extremely subtle and difficult to see. Concentration is one of the tools needed to be able to see this difference. Deep concentration has the effect of slowing down the thought process and speeding up the awareness viewing it. The result is the enhanced ability to examine the thought process.
Concentration is our microscope for viewing subtle internal states.
We use the focus of attention to achieve one-pointedness of mind with calm and constantly applied attention. Without a fixed reference point you get lost, overcome by the ceaseless waves of change flowing round and round within the mind. We use breath as our focus. It serves as that vital reference point from which the mind wanders and is drawn back. Distraction cannot be seen as distraction unless there is some central focus to be distracted from.