"surprise" party: is it possible?

A friend of mine planned to give a "surprise" birthday party to her husband. She wanted it to be all "hush-hush", that everything will be under wraps and that her husband should really remain clueless 'til the party hour. I had doubts about this because how can one keep this kind of "secret" from someone close to you, or someone living in the same house, etc. It just wasn't possible, I told her. But she pushed through with her plan only to be surprised herself by the celebrant when he actually found out about it himself by accident when he chanced to take a peek at the venue earlier that day, where he saw his name and photo plastered on the backdrop of the stage. So? How can one truly have a "surprise" party for someone so close to you?