The tragedy is when you've got sex in the head instead of down where it belongs.

The line contrasts embodied, instinctive sexuality with sexuality that has been over-intellectualized, moralized, or turned into obsession. Lawrence frequently argued that modern life (and modern “mental” culture) distorts natural desire by dragging it into the realm of abstract ideas—where it becomes anxiety, prurience, or power-play rather than a lived, physical relation. Read this way, the “tragedy” is not sex itself but the displacement of erotic life into the head: fixation, shame, and theorizing that sever feeling from the body. The remark also reflects Lawrence’s broader critique of modernity’s split between mind and body, urging a reintegration of instinct, sensation, and thought.