Sin = not noticing

Today my morning devotions/meditation (The Ignatian Adventure: Experiencing the Spiritual Exercises of St. Ignatius in Daily Life) had a reading of Matthew 25:31-46. You know the passage: Jesus talks about the final judgment, separating the sheep and the goats. Then he tells them "I was thirsty, I was hungry, I was a stranger, I needed clothes, I was sick, etc." and the people ask, "When did we see you thirsty, hungry, a stranger, etc.?" The Lord answers, "whatever you did / did not do for one of the least of these, you did / did not do for me."

The devotional said, "Consider how Jesus portrays sin as a failure to notice and act." I had never thought of it that way. A failure to notice. Who am I failing to notice??