Most people would never know the true struggle of having one eye unless they experienced it themselves.
The people Desmond saw after being injured often said "At least you still have one eye". Yet there was no 'at least' for him.
No one considered his lack of depth perception in day-to-day tasks. He moved slowly most of the time to avoid mistakes. Many couldn't ever understand having a large blind spot and lack of peripheral vision that made him paranoid constantly.
If someone watched him for only minutes, they would see his head dart around occasionally, hoping to prevent anyone from sneaking up on him.
The most paralyzing side effect of having one eye was the strain his remaining eye had on it constantly. If he read for too long, the headaches were excruciating. If it was dark, he felt practically blind.
