Good Riddles

Question: What goes up and down the stairs without moving?

Question: While you were folding a letter I got you.
Usually you will do whatever it takes to avoid me,
but now you can't help but find me.

What am I?

Question: A man was able to avoid getting stuck alone on a deserted island by forgetting to put one thing on the island.What did he forget?

Question: There was once three trees. The first tree did whatever the third tree did, and the third tree did what ever the second one does. What happens if tree number two gets cut down?

Question: 1 is 3, 3 is 5, 5 is 4, 4 is universal. 2 is 3, 3 is 5, 5 is 4, 4 is universal... how is this possible? (What is the rule to this sequence of numbers?)