Self-worth/esteem is what we know/think of ourselves. At first we may take parents words for things/how we are but the more experience we get and the more we pay attention to our experience, the better able we are to judge ourselves for ourselves. A father who says something like "my son is so smart, just a chip off the old block I guess!" is not taking a child's self esteem, just adding to their own perhaps. It would be the son who hears it backwards, hears, "I am so smart, it allowed me to have a son just like me" instead of "my son is smart, just like I am smart". Other people's smartness can not add to or negate my own sense of how smart I am, just my own perceptions.