We had one very bright but dyslexic engieer at Cambridge Instruments,
who never really got the idea that it mattered how you spelled a word
as long as what you wrote sounded right, so he used "their", "there"
and "they're" as if they were interchangeable, and - while he
appreciated the theory behind our complaints about his spelling, he
never took us really seriously, because he couldn't imagine that we
didn't hear the words printed on the page.
I offered to spell check his written output on a number of occasions,
but he never took me up on it.
One of the things that you learn being dyslexic, is miss spellings are
frequently valid words in the dictionary, and that spell checkers are
marginally useful at best.
"their", "there" and "they're" are all valid spellings, and spell
check is useless.
I know when I write, I internally know what I want in correct english.
What the brain writes thru my fingers and seen by my eyes is quite
frequently different. Especially when tired, stressed, etc. One example
is that I frequently will replace a word with the word that follows it,
such that it's there twice. Or that a completely different word will
pop out ... such as replacing "the" with "and", or "this" with "there",
or "that" with "this".
I proof right over these mistakes when writing most of the time. If I
wait about 3 days, and reproof, I spot it immediately. Frequently, what
comes out my fingers will be the wrong suffix for a word construction,
such as "confident" will be replaced with "confidence". Transpositions
are also a problem, but for some reason they are a little easier for me
to spot while writing, but not always. This is one area where spell
check makes a difference, some times.
I worked for a boss for several years that was worse than me. We used
to proof each others writings. Only about 50% of the time could we spot
the others mistakes, the rest of the time our brain would automatically
correct their mistake too, and continue to do so every time we reread
that section. Then, for whatever reason, several days later it would be
obviously wrong if proofed again.
I realize that your coworkers actions may have seemed, indifferent.
That in your mind, these kind of mistakes are just careless. But again,
your brain isn't wired that way.