If you can't sleep, then get up and do something instead of lying there worrying. It's the worry that gets you, not the lack of sleep.

The quote distinguishes between sleeplessness as a physical state and worry as the real source of harm. Carnegie’s point is pragmatic: lying awake amplifies anxiety, which in turn makes sleep even less likely; action interrupts that feedback loop. “Do something” does not necessarily mean strenuous work, but any purposeful step—reading, writing down concerns, planning tomorrow, or a calming task—that shifts attention from catastrophic thinking to manageable activity. The underlying message is that agency reduces distress: even if you cannot immediately control sleep, you can control what you do while awake, and that change in posture can lessen the psychological toll of insomnia.