There's something big you want — bigger than your pocket money can stretch to in one go. So you started a jar. Every week a little goes in, and slowly the pile has been growing. You can see it getting closer. Today you're at the shops and there's a smaller thing right in front of you. Not the big thing — just a quick, fun, want-it-now thing. You've got exactly enough in your pocket. But the money in your pocket is the money that was meant for the jar this week. The big thing is still weeks away. The small thing is right here, right now, and your hand is already moving towards it. Nobody would even know.