Unless you specify keys when using list() it expects the array being fed into it to start at 0.
So having the following code will result in a notice level warning "Undefined offset: 0" and variables not filling as expected
<?php
list($c1, $c2, $c3) = array [1 =>'a', 2 => 'b', 3 => 'c'];
var_dump($c1); // NULL
var_dump($c2); // string(1) "a"
var_dump($c3); // string(1) "b"
?>