All that Glitters is not Gold
This is a very popular and well-known saying and we need not search too deep to discover its meaning. It means exactly what it says. Just as anything made of shiny yellow metal need not necessarily be gold, everything that appears attractive on the surface may not necessarily be so in reality. All valuable objects may not look so either. In the same way, a person might look and behave in a kind and generous manner while actually being miserly and mean.
An innocent exterior often hides a wicked heart and a scheming mind, but the reverse can also be true. A hard exterior sometimes hides a soft heart. Beauty is only skin deep and we should strive to be known for our good deeds rather than our good looks.
Outward appearances are often deceptive. We should not judge. people, things, or situations merely by what we see. We should cultivate discerning minds and decide accordingly.