bb on "How counterbalancing errors automatically corrected in the next period?"

Can anybody please explain to me how the counterbalance errors will automatically correct in the next accounting period?
using inventory as an example, when ending inventory is overstated, Net Income for current year will be overstated, and next year NI will be understated.

I understand why current year will be overstated.
Beginning
+Purchase
-COGS (U)
-------------
Ending (O)

When COGS understated, NI will be Overstated.
Revenue - COGS (U) = NI (O)

For next year, isn't the NI will be also overstated?
Beginning (O)
+Purchase
-COGS (U)
------------------
Ending (O)

Can anybody shed me a light why next year NI will be understated if the current year NI is overstated,
I do not understand the auto correct concept.