Let there be no confusion on the issue: I am a whore for pattern mixing. Not to give myself too much of a pat on the back, but I think this is a behavior exhibited and enjoyed by most advanced dressers. Managing to combine a gingham shirt with a paisley tie and a polka dot pocket square is a skill that takes a lot of time and practice to cultivate. Given that I've spent more time cultivating this skill than balancing my checkbook or learning to cook something that isn't Velveeta macaroni and cheese, I'm usually very happy to show it off.
There are times, however, when the concept of KISS (Keep It Simple, Stupid) is called for. My girlfriend's workplace had a small open house a few days ago, and I figured that a little discretion was called for when meeting her boss and co-workers. Since I take "discretion" to mean "take it easy on the lavender socks and blue handkerchief with pink medallions," I opted for something a bit more sober and stuck to solids: a white dress shirt, navy blue tie, and grey merino wool cardigan. Dark, slim jeans and chocolate brown dress loafers rounded everything out, though I couldn't help myself with some argyle socks. Whatever. Sue me.
Wearing so many neutral solids at once had the additional benefit of reminding me that no matter what else, fit is king. Period. A simple but impeccably-fitted outfit will always look better than an ornate one that doesn't conform to the body properly. Never stray from that concept.