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 one with the highest expected value.
Let's say the reward for being right is 100 dollars 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 dollars and, if you multiply the penalty by the probability of being wrong (40 percent) you get 40 dollars. If you subtract the penalty from the reward, the difference is the expected value, which in this case is positive(+20 dollars). Once you understand expected value, you also understand that it's not always best to bet on what's most probable.
作者的意思是说我们做每一个决定时，可以把它当成一次赌博，在下注之前要计算一下预期收益，选择收益最高的下注方式，收益最高的下注方式并不一定是最可能赢的下注方式。
举个例子，假设你有一个赌博的机会，只要你下注100块钱，就有20%的概率赢下1000块钱，80%的概率输掉你的赌注，你到底赌还是不赌？
让我们用作者推荐的方法在赌和不赌之间做个决定，
1. 赌:预期收益 = 1000 * 20% - 100 * 80% = 120块钱
2. 不赌:预期收益 = 0
所以我选择赌！
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