Why does eastward jet lag feel harder to adjust to than westward jet lag?

Answer: Our body clock runs longer than 24 hours

Earth rotates eastward — Wrong. Earth's rotation direction is irrelevant to the difficulty of adjustment. The key factor is the natural period of our internal body clock.

Our body clock runs longer than 24 hours ✓ — Correct! The human body's internal clock naturally runs slightly longer than 24 hours, averaging about 24.2 hours. This makes it easier to delay (stay up later, as needed after westward travel) than to advance (go to bed earlier, as needed after eastward travel). Eastward travel requires advancing the clock, which fights against our natural tendency, making adjustment harder.

Morning light is weaker — Wrong. Morning light is actually a strong cue for adjusting the body clock, but its strength doesn't explain the asymmetry. The difficulty comes from the body's natural tendency to prefer a longer day.