The size of the chances varies wildly.
There are times it makes sense to do the high-risk ones: devs that are unproven, without great academic and work backgrounds, looking to get a foot in the door. Companies that are not well funded looking to find diamonds in the rough, since they can't attract people who already have proven themselves. I've been that dev myself, based just on a strong sense of how the CEO and myself were on the same page based on our conversations.
But it's definitely not a risk I'd take again from where I am now. At a more established place with people I know who vouch for the folks involved, there's a much lower chance of a new FTE getting canned within a few months for anything short of egregious behavior.