A sponge, needle, scalpel, clamp or other surgical instrument can be left inside a patient for several, sometimes compounded, reasons.
First, a large number of objects get used during even simple procedures. Surgeons, nurses and aides can simply lose count of, say, how many sponges (actually, rolls of gauze) they have inserted and removed while trying to control bleeding.
Another problem is that many surgical implements are delicate. A piece of a fine blade or the tip of a narrow-gauge needle can break off without people noticing.
A third issue is that surgical suites can be loud, crowded, confusing and high-pressure places. Even when checklists are used and when surgical teams have worked together for some time, oversights can occur.
Regardless of the exact reason a surgeon and members of the surgical team leave objects inside patients, such errors constitute clear cases of medical malpractice. Patients harmed by retained surgical instruments deserve compensation.