That's too simplistic. It's not the same for everyone, not to the same degree, and people seem to be able to develop something akin to 'VR legs' (though there is the question whether they'll want to stick with it until they do). Added to which, by now developers have a bunch of tricks that can mitigate and minimise nausea, plus Thief is a relatively slow, methodical game for the most part, which helps a lot. There are also various different ways of doing movement in-game that can be experimented with.

Personally, I wonder which aspects of first-person VR play are the most prone to causing nausea. While I've mostly been okay with it (i.e. I almost never feel any discomfort, and it's been like that from the beginning), fast, slidey movement is probably less than ideal, and for me at least it makes a huge difference whether I play sitting and turn using the controllers or whether I stand (my preferred way of playing) and turn by, well, turning.