Earlier quoted context omitted.
Do people pretend to be sick to use up their X days? Many people want to have as many days off as they can. If so, you could be in the same situation, call in saying your sick to use all your days then really get sick at the end of the year. If the answer is no, perhaps that is due to cultural differences. It's my impression that folks in Norway are more responsible in many regards compared to Americans.
There have been studies of this in Finland. When companies require a doctor's note for any and all sick leaves, people will use the maximum amount the doctor prescribes (usually they just slap 3 days on for every sniffle). On the other hand when people can take a handful (1-5) sick days freely, they tend to use just the bare minimum. It's a matter of trust. The company is communicating to the employees that it trusts…
At one of my earliest jobs, I would take a short lunch at my desk (I was very young and didn't know better). Management decided that they wanted to gauge how long I was lunching for, and insisted that I clock in and out for lunch. Well, you can be sure that I took the full time allotted to me after that.