Restrictions are sometimes for safety, as is the case with my daughter, or for mastery, as with Houdini. Mastering the Self is mastering the chain; picking the lock of your own prison. However, one of the biggest reasons for chains is fear. Fear of intruders, fear of being overtaken, fear of injury, violence, or death...even the fear of our own freedom. Chains make us feel secure and safe, separated from would-be intruders and threats. If we don't learn when it is safe to unchain the door, though, we can keep out the friends with the foes, block out the good with the bad. We need to master the chain that binds, so to speak. Like the door chain, these tethers are usually unlocked more often than they are broken. Some chains are damn near unbreakable, and the only way out is through the lock itself.
Chains are used to contain, restrain, restrict, block, and hold. They are also used to lift, to raise, to pull through, and to hold together. They can lock in as well as lock out, sometimes simultaneously. It protects as well as restricts; it goes both ways. The protection is a restriction, but also the restriction is the protection. THAT is a metaphor.
Are we chaining out threats to our well being, or are the chains themselves a threat to our well being? It goes both ways.