In the quote from Lawrence Durrell's book Clea, it suggests that genuine understanding and growth come from interactions with those who do not reciprocate our affection. When love is returned, it may not challenge or teach us as much as unrequited love, which pushes us to introspect and develop deeper resilience.
This idea emphasizes the value of experiencing unreciprocated feelings, as they often lead to personal insights and greater emotional strength. Durrell highlights that meaningful lessons about ourselves are often learned through feelings of longing and unfulfilled affection.