A theory is an idea, a possibility, a speculation. Practice is action. Theory encourages action to try out or test the theory, and practice provides action to support or dispute the theory. They work together well. My theory was that I could play basketball adequately well at 70 -- not as well as at 30, but still well. Long story short, I got into a basketball game with some guys in their 20s. After clumsily moving around on the court, missing passes and shots, falling over myself and injuring and probably breaking my big toe which still isn't completely healed after 6 months, data indicated clearly that my theory was inaccurate. Theory got me out on the court and got me playing. Practice put the theory to the test and woke me up to the reality that I'm not 30. I don't know whether my theories are true or false until I take action to test them. I can hear what others believe or learned, but I don't know for myself until I test the validity of my theories for myself. There is no teacher like personal experience/practice/action, even, maybe especially, when it hurts.