NEGATIVE EMOTIONS - Dalai Lama

If you let negative emotions and thoughts arise inside you without any sense of restraint, without any mindfulness of their negativity, then, in a sense, you are giving them free rein.  However, if you develop mindfulness of their negativity, then when they occur, you will be able to stamp them out as soon as they arise.  You will not give them the opportunity or the space to develop into full-blown negative emotional thoughts.

Dalai Lama