When mindfulness of the Heart is going well, cause and effect can be followed quite clearly: the manifestations of mental activity being clearly seen there.
When things go wrong however, the attitude of something being wrong furthers agitation. Any attempt to correct the situation results in an accumulating deterioration; objectivity diminishes, subjectivity strengthens it's hold: Kammic legacy.
However, just noticing this causal predicament, in it's smallest detail, results in immediate relief. This fundamental Knowing is the exact correction required, the Citta is once again in it's basic mode and healing immediately resumes; objectivity returns: Kammic destiny.