Because you can't have bone-shattering orgasms all the time. If you did, you'd never leave the motel room, things wouldn't get hunted, people wouldn't get saved, and the family business would go to hell. A follow-up to Mine. Sam/Dean. This means Wincest.

Scent is a powerful trigger of sense memory. Sam breathes in the scent of coconut and spice from Dean's shampoo, and remembers that summer. Sam/Dean. This means Wincest.