An interesting video by Veritasium (previously) explores the nature of risk and how humans perceive it. Host Derek Muller asks people if they would taken an even bet with him on the outcome of a coin flip. Muller then alters the bet, offering increasingly better outcomes to his opponents to see when they would be willing to make the wager.
Psychological literature shows that we are more sensitive to small losses and than small gains, with most people valuing a loss around 1.5-2.5 times as much as a gain. This means that we often turn down reasonable opportunities for fear of the loss. However over the course of our lives we will be exposed to many risks and opportunities and this invariably means that taking every small reasonable bet will leave us better off than saying no to all of them.