I have a drawer full of socks. There are 40 socks of each colour, brown and grey, evenly mixed.
In the morning, when it is very dark, I need to pull out a pair of socks of the same colour.
How many must I pull out of the drawer to ensure that I have at least one pair of matching socks?
Answer: Three socks.
Whichever I pull out first, the second will either match, or I will have one of each, ready for the third sock.