Set an alarm on your phone for 10 minutes. Sit down in a quiet room. Close your eyes. Your goal is to observe the physical sensations produced by natural breathing in your nose for the 10 minutes. Give it your full attention and not miss a single breath, and really feel how each breath in and out feels at the tip of your nose as the air passes it. Easy, right?
Except you will probably find that before long, instead of having your attention on the breath like you fully intended, your attention will be on some thoughts. Where did the thoughts come from? Were 'you' thinking them? Or did the thoughts just arise and steal your attention, despite YOU fully intending to be paying attention to the breath for the 10 minutes? What is then your relationship to 'your' thoughts?