"Lagoon" by Joseph Conrad presents a story of moral dilemma because the hero Arsat must choose between two moral values, differeing in goodnes only in the sense that one risks self and one rewards self. A moral dilemma is defined as a situation in which an agent (the individual responsible for acting) is required by circumstances to perform two or more taks that are equally good and definitively moral. The dilemma--or choice between equal things having moral but unequal outcomes--is that while the agent can perform each taks, no more than one task may be chosen. As a result, whatever is chosen will leave equal moral good unfulfilled.
Arsat is faced with the moral dilemma of choosing between his love for his brother, a choice that would risk self (his life), and his love for Diamelen--his lady love whose name is symbolic of the dichotomy precipitated by moral dilemma (dia- a Greek prefix suggesting passing through, going between parts)--a choice for whom would reward self. Thus Arsat is forced to choose between two equally morally good options knowing that with either choice an equal good will be foresaken. His choice is for his love of Diamelen leaving his love of his brother unfulfilled. Only when Dialmelen dies does Arsat begin to repent his choice, a choice that awoke deep and serious consequences in the wake of his brother's death.