Boys dream about finding an owner, finding a connection with someone that makes them want to have a locked chain around their neck. They fantasize about having someone accept them completely, given a purpose to follow commands. Most don't consider the true consequences of being owned, the complete submission and servitude it requires. Most don't expect their mind to be locked away either.
Only a few masters know how to take absolute control, ones who can work magic into the chain to cut off all control from boys' minds. Once worn around the neck they lose all autonomy, put into complete servitude until removed. With a lock however, it's unlikely to ever come off.
The boys never expect it, thinking they'll still have purview over their actions. It's always a surprise when they first realize they can no longer control themselves, forced to do exactly what they are ordered. They quickly learn they can never disobey, their wants and thoughts slowly disappearing replaced with the need to please their master by the magic woven in the chain.
Their entire purpose solely becomes obedience, only happy doing anything and everything they are commanded. It changes them entirely, anything that brought them pleasure before becoming insignificant to their service. It grows to a point that even if their chain is removed, they won't want to do anything else. They are content knowing that all choices come from their master, that they don't need to worry of what to do and how to act. They are happy being chained for the rest of their life.