Definition
Feeling important is Carnegie's name for the deep, near-universal human need to matter — to know that one's existence and contribution register in the eyes of others. It is not vanity, ego, or the desire to be famous; it is the more elemental need to not be invisible. William James called it "the craving to be appreciated"; Adlerian psychology calls it the need for significance; Carnegie treats it as the master key to almost every other principle.
The distinction from flattery or ego-stroking is that feeling important is satisfied by being seen accurately. Generic praise fails because the recipient knows it could have been said to anyone; specific, true recognition succeeds because it could only have been said to them.
Why it matters
How it works
The need shows up everywhere relationships do. In the moment, it is met by attention — eye contact, full presence, real questions. Across time, it is met by remembering: bringing up what the person said last month, congratulating them on the small win, noticing when they are absent.
What does not work is exaggeration. Telling someone they are extraordinary when they are competent reads as insincere; telling them their competence was specifically valuable reads as true. The recipe is specificity, not intensity. Carnegie's deepest move is to treat ordinary people as if their experience and opinion matter — because they do, and most of the rest of the world has forgotten to notice.