Hendrix probably thought that sand melts and he forgot that the
beginning of his sentence, and the direct subject, was castles, not sand.
Usually we can tell by the way things sound when our subject and verb are not
in agreement, but if you tend to go into your own purple haze, where you might
forget what’s supposed to match, keep in mind that several extraneous words or
clauses may intervene between your primary subject and your verb. And go back
to take the extra time to make sure that your subjects and verbs line up.
Of course, you could always try writing when you're high to increase your creativity, but proofreading when you're stone cold sober!
Sigrid Macdonald is an editor and the author of three books, including Be
Your Own Editor, available on Amazon: http://tinyurl.com/c3az54r