This characteristic of the English language gave rise to spelling reformers movement. They wanted to revise the alphabet so that one letter would correspond to one sound, and one sound to one alphabet, thus simplifying spelling. This is a phonetic alphabet.
If we look at English spelling, it is easy to understand why there has been so much concern about spelling systems. In English, DIFFERENT LETTERS may represent a SINGLE SOUND.
Example: to, too, two, through, clue, shoe
A SINGLE LETTER may represent different sounds:
dAme dAd fAther mAny cAll
SOME LETTERS have no sound
Mnemonic Whole Resign Psychology