Sometimes even the blue sky gets grey: that does not mean that the sky stopped being blue, it just means that grey clouds exist and they come by. Mindfulness does not erase our negative emotions and experiences, but it allows us to become an observer of our life and thus see the bigger picture of what is happening. When we see the bigger picture, we learn to accept the moment we are in. Thus, mindfulness is about accepting what is, without pretending that you are a super-human. No one is bulletproof. Your essence may be zen, just like the sky is blue, but sometimes you will also feel anger, sadness, and confusion. That happens because we get distracted by the clouds. As long as you keep practicing to be present in life and to come back to your center, the sky will clear again. It always does.