A key is read almost entirely through what it unlocks, whether literal or metaphorical — access, opportunity, or the solution to a problem you've been sitting with.
Finding a key you didn't know you had is read as discovering the means to solve a current problem, or gaining access to an opportunity you hadn't realized was available to you. Being given a key by someone else is read as that person granting you real trust or access — worth noting who handed it over, since the giver often matters as much as the key itself.
Losing a key is read as losing access to an opportunity, or feeling locked out of something that matters to you — a job, a relationship, a decision that's no longer fully in your hands. A key that doesn't fit the lock it's meant for is read as a solution that seemed right in theory but turns out not to be the actual answer once you try to use it.
A large ring of many keys, rather than a single one, is read as having multiple options or responsibilities available at once — not overwhelming the way an octopus's many arms can be, but worth being deliberate about which door you're actually trying to open.