First things first: if you read this entry's title and didn't immediately think, "That's what she said," we will clearly never be friends. This is the kind of in-depth sartorial analysis you've come to know from DLAMGD.
In the world of tailoring, a half inch is a mile. This lesson was reinforced for me a few days ago when I picked up a navy sport jacket from my tailor; I bought it a few months back and had the sleeves shortened immediately; I literally walked from the store to the tailor. In a rare instance of imperfection, this tailor left the sleeves about a half inch too long, rendering the garment non-wearable.
I finally got around to bringing it back to him, and the difference is astounding (please pardon the lighting in the pictures). You can finally see the bit of requisite shirt cuff at all times, and it's amazing how much more I enjoy wearing clothes that are properly altered. The lesson here is that if your clothes don't fit perfectly, you're missing out on being flush with confidence in your appearance, which is part of what dressing well is all about. A nice suit might feel good, but a perfectly fitted suit feels like the most elegant suit of armor you could ever don.
The details matter. Get thee to a tailor.