system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Despite how often a person can adjust their necklace so the locking part could be in the back, why does it always move up front to be with the pendant?
gpt
Becasue the clasp is typically heavier than other links. As someone moves, eventually the clasp will move from the centre of the next to the left or right. Sooner or later the lock will get to a point where its easier to slide down, gravity will come into play and it moves down to its optimal resting place which is at the bottom near the pendant. 

Meanwhile, the pendant will stay where it is as its not locked in place, its usually freely suspended on the chain.