Principles: Life and Work

by Ray Dalio

5.6 Make your decisions as expected value calculations. Think of every decision as a bet with a probability and a reward for being right and a probability and a penalty for being wrong. Normally a winning decision is one with a positive expected value, meaning that the reward times its probability of occurring is greater than the penalty times its probability of occurring, with the best decision being the one with the highest expected value. Let’s say the reward for being right is $100 and its probability is 60 percent, while the penalty for being wrong is also $100. If you multiply the reward by the probability of being right you get $60 and if you multiply the penalty by the probability of being wrong (40 percent) you get $40. If you subtract the penalty from the reward, the difference is the expected value, which in this case is positive (+$20).

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