Door

Look on every exit as being an entrance to somewhere else.

~ Tom Stoppard

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And look on every entrance as being an exit from someplace.
And look on every window as a place to look away from or toward something.
And look on every ceiling as something over your head or under the feet of your upstairs neighbors.
And if those neighbors slam doors a lot, it doesn't matter if those doors are entrances or exits, that door slamming is REALLY annoying!