Taking the question literally, the answer is that because in this kind of system there's plenty of incentive to lie to get the maximum number of days of paid le

Taking the question literally, the answer is that because in this kind of system there's plenty of incentive to lie to get the maximum number of days of paid leave. So if you're in charge of scheduling employees and you assume that they're self-interested then you would assume that left to their own devices a lot of them would probably lie about being sick. I mean, it's a lot safer assumption than assuming that everyone in the rank-and-file takes some great pride in the success of the company and would never do something morally dubious.