This quote is so true, it made me stop, grab it then read it again. To me this means allowing external factors to control your emotions; worrying about things you have no control over, getting angry about things you have no control over. If you allow yourself NOT to be in the present moment, stress over events past, rather than worry about now.
Giving power, what does that mean? Allowing it to get to you, allowing it to occupy valuable time in your mind which detracts you from thinking about NOW, and what you CAN control.
We are all guilty of it, but the skill is recognising when you are doing it, and being able to recognise that and correct it. 🙂