The phrase "Be liked and you will never want" is basically Willy Loman's credo of life. The premise is that your looks or what you represent to be, is more valuable than who you actually are as a person. Therefore, once you achieve a reputation and get people to like you, you will always be popular and people will always prefer you.
Because the man who makes an appearance in the business world, the man who creates personal interest, is the man who gets ahead. Be liked and you will never want.
This so-called philosophy constitutes the construct that Willy has invented for himself, as well as for his children, which will dictate the choices and behaviors that they all later on. Willy claims to be thankful that his children were "born like Adonises", and places more weight on that than on his children's intellect, life skills, or even their behavior. This shows the shallow nature of Willy Loman as a person and as a parent. What Willy Loman does not seem to realize is that if only the visible and the superficial is what matters, then there is always the danger of losing such looks.
We know that this plan does not work for anyone; not for Willy, nor for his children. The resulting product of all this is Biff, who has lost himself to Willy's ideal, and Happy who equally walks through life clueless as to what to do with himself.