No so DrugCrazed,

That is why you have key signatures.

If a song is in the key of Gmajor, it will have an F# in it.

Instead of putting in the sharp every time you get to an F, you just put the # att the beginning of the stave.

Someone who can read sees one sharp and knows to play the tune in the key of G.

The music on the stave will have no sharps or flats in it unless it goes into a different key.

Most folk is in one key and the chords are all in that key, so the nightmare you have imagined wouldn't happen.

In complex music like Jazz, you will find more sharps and flats written, but you need to start with basic literacy before moving n to tat stuff.

Its all about familiarity.

When a child learns to read, they read out loud without giving the words any feeling. After years of reading, they can read in their heads and "hear" the book vividly.

Actors can look at a script and as they read it they hear the voice of the character and are able to give the words feeling and depth.

Music is EXACTLY the same.