"Try not to think about a pink elephant" someone says.
The first thing that comes to one's mind upon hearing that statement is ironically the very image of the pink elephant which one was supposed to forget about.
We are just naturally conflicted creatures, even our minds work that way. I guess to forget about something (often unhappy events) it is better to just leave it then force oneself to forget, since our minds work in that ironic manner.
The pink elephant concept came from the radio in case you're wondering.. haha.