considering how ethics should not use mathematics. In his influential book Reasons and Persons (1984), the philosopher Derek Parfit considers several misguided principles of moral mathematics. One is share-of-the-total, where the goodness or badness of one’s act is determined by one’s share in causing good or evil. According to this view, joining four other people in saving 100 trapped miners is better than going elsewhere and saving 10 similarly trapped miners – even if the 100 miners might be saved by the four people alone. This is because one person’s share of the total goodness would be to save 20 people (100/5), twice that of saving 10 people. But this allows 10 people to die needlessly. The share-of-the-total principle ignores that joining the four people in saving 100 miners does not causally contribute to saving them, while going elsewhere to save 10 miners does.
Another misguided principle is ignoring small chances
How my heart sings 