To maximize impact you again should spend money not on the hardest problems, but on those where the money has the biggest impact. It's the definition :) Consid

To maximize impact you again should spend money not on the hardest problems, but on those where the money has the biggest impact. It's the definition :) Consider two problems: one makes everyone's life 5% better and costs $100 to solve. One makes lives 20% better and costs $1 trillion. You have $100. Where does your money have the biggest impact? This is malaria and climate change.