Many of us are programmed to try to rid ourselves of sadness and stress when that happens. And often, the way we rid ourselves of those uncomfortable emotions is to reach for an activity, food, drink or individual that makes the uncomfortable feelings go away. Yet, if we learn to identify those feelings, then sit with them for a while via mindfulness or another kind of reflection, we'll find that those feelings are simply feelings--feelings that we can live if if that's what we want or need to do.
For example if there's a sadness in your life, a sadness you have no control over, you can learn to simply live with that sadness and/or give that sadness a place in your life that's not harmful or hurtful. The same can be true for stress--if you cannot rid your life of that stress, you can learn to live with it.
In the end, learning to live with these feelings is a lot better than ignoring the emotions or burying the emotions. Finding ways to do this effectively can improve your life. Onward.