[klodolph]

Most people can tell the difference between /naʊ/ and /nɑt/. I mean, just look at them... one ends with a consonant, one doesn't, and the vowels are reasonably different.

The difference here is between /faɪl/ and /ˈfaɪəɹ/, which is much more subtle. It comes down to the difference between /l/ and /əɹ/. The [ə] is an uncommon vowel in languages, unstressed, and mostly subsumed by nearby sounds. And worse, more than a billion people on the planet grew up speaking a language which doesn't distinguish the [l] and [ɹ] sounds (they're both approximants with only slight differences in articulation). So when you say "file" or "fire" these people can't distinguish which one you're saying, and when they say it they use something like the tap [ɾ] or retroflex [ɻ] instead, both of which sound ambiguous to native English speakers. Or some non-native speakers will use [l] exclusively, for both /l/ and /ɹ/.

[jpatokal]

FWIW, while Japanese doesn't distinguish L and R, "fire" is transliterated as ファイア faia while "file" is ファイル fairu. So the difference is reasonably clear.

[klodolph]

The difference is only clear after transliteration. The problem is that transliteration is difficult to begin with.

[lazharichir]

That's very scientific but most people will read it, not write it. And most people will use one, and not even acknowledge the existance of the other.

Sure, they are one-letter away from the other, it's a fact. But to turn this into a problem, well.. no...

[jfrankamp]

The parent gave a phonetic explanation that has nothing to do with writing but rather hearing and speaking about it. For a billion people they aren't one letter away from each other, they're ~ the same. That's the point.

[klodolph]

This is a problem if you work with an international team, especially if you talk over video links which are usually less than ideal.