The speaker describes the small lie most of us tell daily: answering "I'm fine" when we aren't. Nothing about it is real. The smile is fake, it doesn't reach the eyes, and the words come out smoothly because they've been practised so often. The person asking is easily convinced and stops looking any closer, happy to believe nothing is wrong.
What makes the poem interesting is that the speaker isn't simply complaining about being misunderstood. The disguise works, and it even feels protective. Hidden behind it, the speaker is "safe" and can't be hurt by anyone. But the last line turns on that comfort with a blunt question: "at what price?" The poem suggests the cost is loneliness, since no one can help someone they never see.
The mood is quiet, weary and a little resigned. Short, steady lines with simple rhymes mimic the rehearsed script they describe, until the closing question breaks the calm.