Wow! I just came back from an awesome talk during my monthly retreat at my parish. This great person came and talked to us about being sincere and truthful. She explained how the word "sincere" had its roots on several theories that have been advanced to explain the derivation of the word, but none has been substantiated!
The most common explanation assigns the genesis of the word to the Latin sincerus, meaning "pure" or "clean", but many etymologists state that sincere is a compounding of sine cera, which means "without wax". According to this "folk etymology", in the time of the ancient Romans, devious dealers in marble and pottery would conceal defects in their products by filling the cracks and holes with wax. Honest merchants, who did not doctor their products, proudly displayed their wares as being without wax; that is, they were sine cera. I found this explanation to be enlightening and amazing, because if you think about the times when you have had to tell a lie, it usually is when you want to show something that you are not. You are most likely covering imperfections.
Every word we say and everything we do is a reflection of our own heart and conscience. It is very important to fill our inner life with good things, with God, good things to read, good intentions, good and positive thoughts - so our acts will be a reflection of the true good heart that we have worked on.
Sincerity gives us freedom to be the true person we are, to accomplish the projects we would like to see accomplished, to be the abnegated mother, lover and friend that we want to be. The truth goes together with the "why". Why am I serving this breakfast? Why am I taking my children to the park? In the answers we can see if we are acting only because "that is what moms do", because "I have to" or because "I love to see my children grow and play because I really want to."
Whoever gives love, time, comfort, can't go around asking for payback, because nobody told you to do so, you did it because you wanted to do it. If you are doing things for the wrong reasons you are being a hypocrite and that can't make you happy.
When we talk with our kids, specially our teenagers and find out that they are sad, uncomfortable with themselves, displaying low self esteem, then we should work, not only on their outer selves: the clothes, weight, lack of exercise, but most importantly, we have to help them find out their "whys". We have to help them find out what is really inside of them; help them be truthful to themselves, help them peel away the wax.