That is the whole point.
If you need to drive tomorrow, you don't risk losing your licence by drinking the night before.
You can think of a million reasons why you may fail a breath test after only consuming a small amount several hours earlier, but if you have zero units of alcohol, you won't have the worry about failing or losing your licence.
The whole 'I'll be fine' mentality is the exact issue. You drink and then get into a car with impaired judgement believing you are ok, when you never really know unless you haven't drank for approx 24 hours.
Don't risk it.
The way I look at it is simple.
If I drink and drive, what could be the outcome?
An accident where I kill or injure myself/others. I lose control and damage my car and other property. I get pulled over and fail a breath test losing my licence. I lose my licence and can't get to work, so lose my job. I can get to work, but have to use a Train/Bus/Taxi/Bike/Walk in all weather at greater expense. I have to pay to retake my test and then fork out for higher insurance premiums.
All of those scenarios (and there are others) come with an increased cost of my daily living, or removal of my freedom.
For the sake of drinking a soft drink or paying for a cab home, I think the choice is a 'no-brainer' and anyone choosing to risk driving after a drink is a complete idiot. Nobody is forced to drink. Anyone that can't resist a drink should know in advance to leave the car home. No excuses. Ever.