There is a time when members of the Thieves Guild have to take the Test.

Its a measurement of skill, speed and wits:
Picking a lock in mid air, as the maggots are surprisingly quick when it comes to chasing prey.
Evading the flesh eating maggots, and finding your way out of the pit.

Sadly the thieves have some mischeavious members in them.
It seems that this particular thief's picklock was replaced with something not as strong as a normal picklock should be.