This is one of the sadder reasons why scheduled aviation is so safe. When flying planes is your job, why would you ever push your luck? I feel so tired, that storm looks pretty nasty, or the maintenance guy seemed like he had no idea why it's doing that - fuck it, we're not going, get the airline to put you on another plane if there is one, otherwise get them to pay for your hotel, I'm not flying anywhere today.
One safeguard that is needed, and I believe is provided even in the US - is a strong union to ensure that "Because I'll get fired unless we go" isn't the answer. People in safety critical roles must be protected so that "No" is always an option for them.
For private pilots, reasons to push your luck sneak over from real life. To get home before the twins are asleep. To be back in time for work tomorrow. So that I don't miss Trisha's wedding. Because the replacement was very expensive and I can't afford it right now. The fuel prices are lower back home, we'll fill up there.