Well, not quite.
There are spelling and pronunciation rules in our language. In the case of 'osmosis'...the first "O" is followed by two consonants, which indicates the "short-O" (ah) vowel. The second "O" is followed by only one consonant which wants the "long-O" (oh) vowel.
At least that's how Mercun English worked 60-some years ago when I was in grammar school.
Review again later.