Hall of Infinite Doors

You blink for a few seconds. If this door is invisible, how can you see it? And yet, there it is. Or isn't, as the case may be. Are you delusional?

Your hand reaches out, but you touch nothing. Waving your hand in the spot where your eyes see a doorknob, you watch as your hand passes through the solid not-door.

Are your eyes deceiving you? Or has the door changed you somehow? Normally, you don't believe in magic...but, let's face it. You're in an endless hallway.

Still, the question remains. Is the door transparent? Or are you?