It’s possible (for most people) to desensitize one’s self to motion sickness: the key is to stop immediately as soon as you get the slightest hint of feeling sick. Repeated exposure taken slowly can lead to improvement.

The issue is people try to push through it to the point they feel sick, and in doing so sensitize themselves to VR induced motion sickness. Getting over that is much harder to do.

It’s no different from feeling nauseousness from trying to eat something that made you violently ill in the past.