Traveling with dual citizenship (dutch and US) from US to Netherlands, and back [duplicate]

My main confusion is that I've read that you should always exit and enter a country with the same passport (which I am obviously not doing)

You are doing it.

The thing you are forgetting is that exiting country A and entering country B are two separate things (and the airline check-in is a third separate thing). When you exit country A, you should use the passport that you entered country A with (that's the "always enter and exit a country with the same passport"). But that does not have to be the same passport that you use to enter country B (which would be whatever passport allows you to enter country B). And for airline check-in, you should use the passport you will use for entering the destination country (which you have correctly described).

Note that the US does not have exit checks, so the "exiting" step for the US to Netherlands flight is trivially satisfied. However, for the Netherlands to US flight, you will exit the Netherlands with your Dutch passport and enter the US with your US passport.

As @user102008 explained, what you plan on doing is perfectly fine. But note that you can use whichever passport you feel like when checking in (or even show the airline several passports if needed). This has no consequences and you can always show your EU passport later, at the official passport check at your destination airport.

The US is a little more specific than European countries about all this. If you are a US citizen, you legally have to enter the country with your US passport. Because airlines share the passenger manifest with US authorities and nearly everybody else needs an authorisation, it's also important to make sure the airline does register the details of your US passport when flying to the US.

In the EU, it doesn't really matter. It's easier to use your EU passport when entering the UK or the Netherlands so that you don't get a stamp or questions but that's about it. US citizens don't need prior authorisation to board a plane to the Netherlands and even if you do enter using your US passport, this should not have any serious consequences.