Life's grand mysteries: whiteboard markers

I unabashedly love to ponder life's little mysteries.

Here is the whiteboard - one of my favorite things:

And here are whiteboard markers:

The more colors, the better.

How is it that if one approaches the whiteboard and find five markers, there is a very high chance (70%?) that at least one of those markers are short of ink?

Why hasn't the previous person thrown them out?

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I don't know the answer. Here are some guesses:

1) Markers run out of ink frequently. In fact, they ran out of ink between users. The previous person actually had enough ink. It was bad luck that the pens ran out just before I picked them up. (This is the only answer that doesn't involve psychology.)

2) The previous person was too lazy to walk toward the trash can / waste basket. Let the next person deal with it.

3) The ink was not completely out. It wasn't good enough for me, the previous person thought, but it might be good enough for the person after me!

4) It never crossed the previous person's mind that the markers should be tossed. It's like going to the supermarket. You pick up an orange, and see a black spot on it; you put it back and buy another one.

5) The protocol is always for the next user to throw pens out. I am just blissfully unaware of this protocol.

What do you think?