离 (traditional 離) began as a bird tangled in a catching-net — the moment of breaking free. Departure has flight built into it: to leave is to slip the net.
离 measures separations: 离这儿远吗? (far from here? — the distance pattern 离…远/近 every learner drills), 离开 (to leave), 离婚 (divorce). Chinese poetry made 离别 (parting) its favorite sorrow — the Tang dynasty ran on farewell poems at bridges and willow groves. In the I Ching, 离 is the trigram for fire — clinging brightness — softening the sadness with light.
The bird slips the net — LEAVING; the gap it leaves is DISTANCE.
Willow (柳 liǔ) sounds like 留 (stay) — so Tang farewells came with willow branches: a pun begging the traveler to remain.