Key?

What sort of key are you? I got this from sistercdr.

You actually don't unlock anything; you're the
winding key for an old grandfather clock. Few
people know how important you are unless you
aren't there, but there are a few who treasure
you all the time. You help people keep moving
forward, but you also help them through the
present by reminding them of the past.

What sort of key are you and what do you unlock?
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