The classic men's jacket is a classic wardrobe piece for a reason. It makes any man look respectable. Think about it. Pair a well-tailored jacket with classic shoes and sharp trousers, you've given 90% of your body a time-tested, solid presentation. All you have to do is brush your hair and smile!
The single men's jacket, buttoned near the waist and ending at the bottom of the buttocks has endured for a century because it builds out the shoulders, exaggerates the trimness of the waist, and it's solid lines allow the eyes to move up and down the body without being jarred to the right or left.There are specific proportions the human eye finds pleasing. The “golden ratio” and similar mathematical cousins crop up in art across all cultural lines, demonstrating our inherited preference for certain shapes and balances. Unfortunately, most men's bodies aren't built along any kind of ideal ratio, which is why none of us look like Greek sculptures (the ancient Greeks loved them some math). Our waists tend to be right around the midpoint of our height or just slightly above it, which is great for balancing and running away from saber-toothed tigers and other evolutionary needs but not as aesthetically pleasing as something more in the neighborhood of a 1:2 ratio. A suitcoat raises our perceived waistline, dividing our body into a top third and a bottom two-thirds rather than cleanly in half.