It really is as simple as this picture.
If you over eat you will "spill over". Each person will have different BMR (the amount of calories that can be consumed to maintain weight).
If this person is continuously exceeding this number then those extra calories will basically be stored as fat around your body, which in most cases is exactly what we are trying to avoid.
So what can be done?
Stop the glass from over flowing and where possible, take a sip every now and then... have I lost you.
So we know the glass represents your body, the water your excess calories/fat so what if I told you that taking a sip from the glass is you exercising. Now what is very important to understand that just taking sips and not turning down the speed of the water will still allow the glass to overfill and cause progress to not be seen.
The ideal place to be is to have the glass 3/4 full which will allow the glass to fill a little before becoming an issue. Have the water dribbling into the glass and continue to sip where possible. Allow some wiggle room and use a wet floor as a sign to turn the tap down a little before trying to take big gulps.