In 'The Moon and Sixpence', Strickland is referring to the fact that Stroeve rescued a suicidal and pregnant former maid from the streets by marrying her. That required the sacrifice of his social standing. However that sacrifice left his bride feeling indebted to him.
anything that costs him something (not necessarily money). The idea is that by making a sacrifice he has left her with a feeling of obligation that she doesn't want.
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