When you buy a new car, you compare different offers:
Offer A without bonus protection: CHF 1100.–
Offer B with bonus protection: CHF 1200.–
You decide for the cheapest offer without the protection of the bonus. After 3 years, one morning you drive too quickly into a traffic jam and collide with the car in front of you. The following year, the premium increases to CHF 1500.– due to the accident.
Offer A without bonus protection after an accident: CHF 1500.–
Offer B with bonus protection after an accident: CHF 1200.–
With Offer B you would have paid a little more premium earlier - in 3 years the supplement would have been CHF 300.–, but thanks to the bonus protection, the premium would have remained constant even after the accident. Since you have not subscribed to the bonus protection, you are now paying CHF 400.– more - and therefore have to dig deeper into your pockets over the years. If you drive without an accident in the next few years, your premium will decrease again, but it will increase if you have another accident.