A spectator is invited to assist with an experiment.
You hand them an attractive wooden chest and ask them to place it on the floor. The magician then shows the spectator a silk and tells them to imagine that the silk is heavy, very very heavy. The magician places the silk inside the chest as you continue to tell the spectator to imagine it is very heavy.
Next you invite the spectator to lift the Chest. The spectator can NOT lift it! It won't budge.
You now open the lid & remove the silk. The spectator can now easily lift the chest.