suit look sharp because the lapel

Single breast jacket
If you wear a suit it's because you want to look sharp for your business.
When you buy a suit you have to be careful that the suit doesn't make you look bulky or square shoulder looking.For that you have to look at the lapel of the suit, try one with normal lapel and try one with thin lapel and you will see that the thin lapel make you look thiner. The jacket must have a "shape in" on the waist line but this depend on your body as well. The good looking business suit should have as well 2 slits in the back and no a single vent and never believe a tailor whom say that a jacket with no slits or vent look better, it is just easier to make that all.
Willy