The weirdest thing happened to a friend a long time ago (not in the Netherlands though). He had a fancy lock on a crappy bike. The bike was there, but not the lock.

I did that too. Back in university, I'd refurbished a white granny bike I found in the trash. The thick chain lock was the most expensive part of it. It got stolen one of the few times I parked it at Oude Manhuispoort (an infamous bike theft hotspot at a central location of the UvA).

Ever since, I try parking my bike near one that looks better and is locked worse than mine.

Yes. Another point is that even when you lock your bike, thiefs often carry the bike in its entirety or just screw off one of the wheels. Just don't buy a new bike when you're frequently in a hot spot.

Locking just a wheel is a rookie mistake, of course! Always wrap it around the frame and something that is solidly rooted in the ground.

It's just that even all that isn't always good enough if the homeless guy or professional bike thief has a power-cutter thingy.

My sister locked her bike to a pole through the frame in San Diego. When she came back literally every other part was gone, and the frame remained locked to the pole. They even took the cranks, the forks, and the brake cables. Who steals brake cables?

I had the quick release clamp stolen on mine (after taking the seat off). Twice in one week, because i happened to have a spare. And the window wipers from my car one time.

I saw a bike chained to something once, little foldable bike, with the saddle missing. It dawned on me later that the owner probably took it with him, to make it less attractive to be stolen.

That, or the seat got stolen. Some people have an odd sense of humor.

A good leather bike seat can be pretty valuable on its own.

Especially if said thief had previously stolen a seatless bike.

The people who steal a frame somewhere else. Otherwise they can not finish their bike...

Yeah I left my bike at work and someone decided he had more use for my rear lights than me. Who steals 5€ lights?!

Somebody who needs it and has a criminal attitude. It's 5 Euros for free, like a banknote on the sidewalk.

Also use 2 different locks, like dLock and a cable lock.

Create bike Safezones, by adding a small plasti foil bag with fish-oil beneath the saddle, which rips if not removed at ride-start. Even bike-thiefs do not want to stink.

Reminds me of that 'prank' video where they left a bike on a steel cable, which the thieves found out the hard way (e.g. after leaving). Oh and another one where they put a tazer in the saddle.

Greasing the handlebars and seat may work well :-)