Mencius criticizes fame-driven hypocrites. Such people may surrender a large kingdom for good repute, yet reveal greed and discontent over trivial food gains, showing hollow virtue fails small, unobserved tests.
What is meant by “making one’s intentions sincere” is not deceiving oneself. It is like hating a foul odor or loving a beautiful color – this is what is called self-satisfaction (or inner authenticity). Therefore, the gentleman must be especially vigilant when alone.