A simple but extremely effective technique that allows you to force ABSOLUTELY ANYTHING.
A list of items written on a business card is handed to your spectator. They hold this card behind their back and commit to one of the items, sight unseen, by marking the card with a pen. Whilst still behind their back, they fold the card again.
You then ask them to place this card under the pocket clip of the pen, and hold onto it until the very end of the routine.
You can now continue with the effect, safe in the knowledge that when your spectator opens that card again, they will see that they have marked/chosen the exact item you needed them to!
This force WORKS EVERY TIME. The super simple method also allows you to concentrate more on your presentation, to give your audience the best experience you can.