The man would still take what was his neighbour's, but his conscience would not be so much shocked. So, equivocation is a more subtle sin than direct lying. In like manner a person who does not intoxicate himself, may eat too much. Gluttony is a more subtle sin than drunkenness, because it does not show so much. And again, sins of the soul are more subtle sins than sins of the body.
Infidelity is a more subtle sin than licentiousness.
Even in our Blessed Lord's case the Tempter began by addressing himself to His bodily wants. He had fasted forty days, and afterwards was hungered. So the devil tempted Him to eat. But when He did not consent, then he went on to more subtle temptations. He tempted Him to spiritual pride, and he tempted Him by ambition or power.