And don't buy a bike without knowing the full history and paperwork, otherwise you are shooting yourself in the foot by supporting criminals and raising your chance of having your bike stolen in the future.
This (obviously) precludes you from cycling anywhere you might want to go (home, the shops, your friends houses, a restaurant, a bar, a cafe).
If you restrict yourself to parking in locations with cameras (e.g. stations), your bike will still probably get stolen, especially if it is expensive (I know people who have had their bikes stolen from station bike parks with cameras). I myself had the front wheel stolen from my bike that was parked between 3 CCTV cameras, next to a busy metro station, next to a shop with a security guard, and across the street from the main police station in the city.
That works well as long as you only want to ride between places with secured parking locations with gated access and cameras.
In the US I have noticed a bit of a disconnect between bike hobbyists (put your bike in your car and drive to the place you want to ride) and people whose bike is their primary mode of transportation. I'm sure it's different in the Netherlands, but a lot of places here you're lucky to find a single bike rack near your destination. "Secured parking locations" don't exist outside of the occasional upscale apartment complex.
I can sadly say from experience that this does not help when you live in student housing.
Also, one lock? You've been lucky. Two locks of different brands is a better bet (junkies tend to specialize in unlocking one particular type quickly)