php require() will die if the included file has a syntax error even the error line is not executed(i.e., within a function that is not called)
for example:
file1.php
<?php
function(){
$data['username']="myprogrammingnotes.com";
echo "$data['username']";}
?>
file2.php
<?php
require_once("file1.php");
?>
Because echo statement has a syntax error(cannot contain an arrray item in a string), file2.php will die.