"
Cain't" is not the same as "can't." "Can't"
as you know is a
contraction for "cannot." Adding the "i" means that whatever cannot be done is WANTING to be done but is impossible to do so. It "ain't possible." and this is usually due to the circumstances surrounding it.
"Now, Milton. I just cain't
get up in that water tower without
the ladder."
"You're saying you don't know who took it, then ?"
"Exactly."