That's the big danger with solar eclipses. It's not bright enough to hurt at the time. The damage only starts to become apparent after a few hours or the next day.
When I went to see a total eclipse I was surprised that even a tiny slit of the sun was still hard to look at. Not sure why anyone would try to stare at that.
galileo (the galileo) used to stare at the sun for extended periods of time (without a telescope), to the point he could identify sunspots. But IIUC he looked at it near the horizon when it's attenuated by more atmosphere.