Why did he beat the lie detector?!? We are very confused!!!?

The lie detector monitors the heart rate, when a person lies, their heart rate increases. But if a person usually lies alot, then their heart rate is usually faster. Then, they get so used to lieing that their increased heart rate is now their normal heart rate so when they take a lie detector test, it sees that their heart rate has not gotten faster and it thinks that they are telling the truth.