Earlier quoted context omitted.
Are you advocating a one-sided view of big decisions?
No, I'm advocating being realistic about your tolerance for risk. If 3-4 years of runway isn't obviously long enough, then you probably don't have the stomach for a startup.
People with 6-figure salaries and 3-4 years runway tend to be calculated risk takers. They don't jump in unless it looks like there's a decent probably of success. That doesn't mean they won't take any risks, just that they want the odds to be in their favor.
All that said, I'd say go for it. You can always get another job, and 3-4 years means you won't be in dire financial straights when you're looking. Starting your own company often uncovers other opportunities that wouldn't otherwise be there if you just sat in a secure day job, too.