Which rules define how to pronounce a consonant? [closed]

My question might appear silly and pointless to some, but I find it pretty interesting myself.

If we look at the word 'circus', it has 3 consonants and 2 vowels. However, the 2 c in the words are pronounced in a different manner. The first has sound of s as in 'hiss', while the second has the sound of k as in 'kit'.

Also, the vowel i and the vowel u are pronounced the same, although they are not the same. Both, in this case, are pronounced as u in 'cut' or 'upper'.

There are even more examples of such confusions, such as the use of ph vs f in 'graph' and 'fish'.

Why is it so? Why is it so that in English, such discrepancies in pronunciations exist? Is it because most English words are derived from different languages, Latin and Greek?

PS: On a side note, I just want to say that in my native language, Hindi, it doesn't happen. Even if such differences do exist and I just don't know about it, they're rare.

The English writing system is at fault and every native speaker knows that.

"In a Garden-of-Eden writing system, you would have a single letter for each speech-sound and one speech-sound for each single letter." Language Myths
German is much more like that than English, and several other languages too.

Although a large number of English words do follow such pattern - best, help, jam, limit, map, win, rob, yet, to mention just a few - most English words prove that there are too few letters for too many speech sounds. The reasons for this have to do with English words having different origins, pronunciation changes throughout the centuries, the difficulties that a spelling reform would face, etc. To have a better explanation, see Language Myths

humour

British worker - "I can't work today, sir. I have diarrhoea."

American boss - "Diarrhea? That's dreadful. You could have sent me a sick note."

British worker - "I can't spell it, sir."