From experience in the projection booth, I can say that all film starts to become a blur, after a while.

I have to inspect anywhere between 6 and 8 reels of film (2,000 ft. ea.) per movie and, at times, I would build build or break down as many as six (or more) movies per week.

After a few months of working like that, you don't even "see" the images on the film anymore. It's all transparent strips of plastic to me, anymore.

I can imagine that people who work in labs would think in a similar manner.