Two reasons to use descriptive variable names

[tangaroa]

Reason #1:

foreach($items as $i){ // $i is an item reference
    ...
    // Now let's loop through something
    for($i=0,$max=10; $i<$max; $i++){ // d'oh

Reason #2:

$dir = $asdf ? -1 : +1; // direction
... 
$dir = getDirectory(...); // d'oh