Appearances are Deceptive
Outwardly appearances are many times deceptive. It is not always correct to make judgment about anything by its exterior appearance. One can't find the real worth of any one just by seeing his external appearances. Not all who looks decent outside are decent inside too. One should be judged only by their characters and not by their outward appearance. In real life situation, many crooks, by their outward attitude and behavior, make themselves appear to be gentlemen and noble people. That is why there is a famous proverb saying "All that glitters is not gold". So in every walk of life, one should always remember that outward appearances may not always be the truth and act accordingly
There is a well-known expression "Don't judge a book by its cover" means that we shouldn't judge other people just by what we see on the outside. We shouldn't be judging someone when we haven't fully known that person, we shouldn't be biased just cause of there looks or where they are from. .Your ideas and thoughts about a person or object should not be based on what you see, usually things like how the person or object looks like physically, what they wear, what they act like, etc. Something can be very different outside than it is inside. Often we base our ideas of something when we first see something, like if one fruit looks more undamaged or fresh than another, most people would immediately think that the better looking fruit is the better fruit, even if inside, the good looking fruit has a fruit worm. A person may look lazy but can work very hard and efficiently when motivated.
People who put trust in people's appearances may learn quickly that their method of trust is wrong. They could put trust into a person who looks well-organized and smart, and find out that "trust" of their appearance is deceiving, and that the person is very different from what the person looks like. Because of their judgment of appearances, they would not get to become acquainted with others that other less judgmental people would get to meet and possibly become friends with them and develop a relationship.
Those that rely on first impressions would find making friends hard as they only rely on their first instincts, usually making the wrong choices, because people that look 'good' might actually be bad in their personality. You have to fully understand something before you jump to conclusions, as looks can be deceiving - a robber may have good intentions, a police may be corrupt.
Those who put their trust in appearances will usually be disappointed later on as they are proven wrong, they will eventually learn to not judge things by its cover. Trusting people by appearance can be dangerous as people might not always turn out to be what you think they are. They could hurt you in the end if you told him things you would tell a trusted friend.
In other words, it means do not jump to conclusions or make assumptions of something by only looking at their surface appearance. It is normal to think of someone like that before you know them, but once you actually know them better, they might be totally different from what you have thought or assumed previously.