The late Pleistocene glacial cycles are dominated by a 100-kyr periodicity, rather than other major astronomical periods like 19, 23, 41, or 400 kyr. Various models propose distinct mechanisms to explain this, but their diversity may obscure the key factor behind the 100-kyr periodicity. We propose a timescale-matching hypothesis, suggesting that the ice-sheet climate system responds to astronomical forcing at ∼100 kyr because its intrinsic timescale is closer to 100 kyr than to other periods.