In tonglen practice, when we see or feel suffering, we breathe in with the notion of completely feeling it, accepting it, and owning it. Then we breathe out, radiating compassion, lovingkindness, freshness - anything that encourages relaxation and openness. So you're training in softening, rather than tightening, your heart. In this practice, it's not uncommon to find yourself blocked, because you come face to face with your own fear, resistance, or whatever your personal "stuckness" happens to be at that moment.
Pema ChodronNobody else can really begin to sort out for you what to accept and what to reject in terms of what wakes you up and what makes you fall asleep. No one else can really sort out for you what to accept - what opens up your world - and what to reject - what seems to keep you going round and round in some kind of repetitive misery.
Pema ChodronEach of us has a "soft spot": the place in our experience where we feel vulnerable and tender. This soft spot is inherent in appreciation and love, and it is equally inherent in pain.
Pema Chodron