Satipatthana Sutta, Fourth Foundation: The Effort to Discern from Seattle Insight Meditation on Vimeo.
What is a skillful or unskillful state of mind? What do those terms mean--skillful for what purpose? Even to know something at this most basic level requires active discernment. The Buddha may have said certain states were skillful or unskillful, but that does nothing for your practice. You have to see its effect on you and know its impact directly.