How it works
A budget is a plan for sharing out your coins across the things you want, so they all fit.
Dev had 12 pretend coins for a party. The cake cost 5 coins, balloons 2, music 3 and games 4.
All four cost 14, which is 2 more than 12, so Dev picked one thing to skip.
A budget shows that before spending, not after. There is no one right budget, just a plan that fits.