I cannot express my frustration at seeing code like this:

if (isset($modifier)) {
    // Do some things.

    // And some more things.

    // Still more
    // things
    // to be done here.

    // There's a whole lot of things here!

    // Last bunch of things
}
else {
    // Do totally different stuff
}

People. Comment your elses! I shouldn’t have to scroll up to read the if again just to figure out what a branch of logic does. This is a maintenance code nightmare, and simply adding a simple “// If validation has failed” will save all kinds of time and frustration.