The explanation of this rests on an elementary lesson in Old English phonology, which it will do the reader no harm to acquire.
The modern symbol _i_ (when denoting the _short_ sound, as in _pit_) really does double duty.

It sometimes represents the A.S.short _i_, as in _it_ (A.S.

_hit_), _sit_ (A.S.

_sittan_), _bitten_ (A.S.
_b{)i}ten_), etc.; and sometimes the A.S.short _y_, as in _pyt_, a pit.

The sound of the A.S.short _i_ was much the same as in modern English; but that of the short _y_ was different, as it denoted the "mutated" form of short _u_ for which German has a special symbol, viz.