As with most of these wonderful quotes - easier said than done. I also feel the quote not necessarily has to have the word 'never' in it. Everybody also has so many happy memories from the past that are energising. I refer to the thoughts that rob you of your power, take away our energy, motivation, enthusiasm, creativity and keep you stuck. These thoughts are well worth learning how to manage. Especially when they do not serve your present moment. I find realising 'what just happened', i.e a thought throwing me back into the past, accepting that it is exactly that 'a thought' and then bringing myself back into the present with a couple of deep breaths works best!
If you are curious to know more about how the past can keep you stuck click to read the short exercise 'Dwelling on the past - Thoughts on how to let go' from Suzie's book 'Balance'.
A Practical Handbook