This idiom comes from an old tale describing a thief who wanted to steal a neighbour's doorbell. He knew that as soon as he touched the bell, it would make a noise which would alarm everyone. So to prevent people from hearing the noise, he covered his own ears, thinking that if he couldn't hear it, no one else could. The moral of the story is that just because you can't see (or hear, in this case) things your way, it doesn't necessarily mean that everyone else can't.