Last time I checked...training can be done goggled or with the Mk I Eyeballs or even with the Mk i's improved with spectacles.
What does happen when NVG's are not used is One realizes just how much One can not see in the Dark.
We did a Training flight down on the south end of our playground where the Trainer wore Goggles and the Learner had his flipped up out of the way but ready to go when flipped down.
We set up a track towards an abandoned Recycling Building with a very large and tall but unlit brick smoke stack....due to there being no electrical power being supplied to the derelict site. At a height well below the top of the Stack and it smack dab at 12 O'Clock to the nose of the aircraft....and at a somewhat uncomfortable distance from impact....the Learner was asked to confirm everything was Peaches and upon doing so....was instructed to lower his Goggles and offer a Second Opinion.
It is scary what you cannot see if you can see it.
Once you use Goggles you will quickly grasp Night Flying is much easier if you can see. It makes thinking in the dark far more easy.