The most exhausting thing in life is being insincere.

Lindbergh’s line frames insincerity not primarily as a moral failing but as a form of chronic labor. To be “insincere” is to maintain a split between inner feeling and outward performance—monitoring one’s words, managing impressions, and suppressing spontaneous response. That constant self-editing consumes attention and emotional energy, producing fatigue akin to living in a sustained state of tension. The remark also implies an ethic of authenticity: sincerity is not merely virtuous, it is sustainable. In this view, honesty with oneself and others is restorative because it reduces the friction of pretending and allows relationships and choices to be grounded in what is actually felt and believed.