The fail-fast contract is 'best-effort', not guaranteed: a case that does NOT throw
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list before: [10, 20] (size=2)
elements the loop actually saw before ending: [10]
list after the loop: [20]
ConcurrentModificationException thrown: false

Why: after removing 10, size becomes 1 and the iterator's cursor is already 1
(it advanced to 1 when next() returned 10). ArrayList.Itr.hasNext() is just
'return cursor != size;' - no modCount check - so hasNext() sees 1 != 1, returns
false, and the loop ends normally. next() is the only method that checks
modCount, and it is never called again. The element 20 is silently never visited.