i strongly disagree with the author. you cant ignore sunk costs.

For example, in the stock market the majority of active retail traders (>90%) get wiped out within 3 years. they continue to dump money into the market, ignoring losses (sunk costs), hoping that the next trade will help recover the losses, and then the next trade, the next ... etc. at some point one has to stop "bleeding" and re-evaluate the approach before blowing out trading account completely. this plays out in the stock market every day and will continue for as long as trading exists. one cant ignore sunk costs - we have to learn from it.