In addition to what others have said here: I’ve seen a total eclipse. The several minutes of total eclipse is preceded and followed by hours of partial eclipse. Even when the sun is 99% covered, it’s still bright enough to damage your eyes. Normally you’re just not going to look at the sun because you both know it’s bad and there’s no reason to. But during the hours before and after the total eclipse, you do have a motive—you’re curious to see the eclipse before it is total. So you’ll look at it more directly and longer than you ever would at any other time, and this will cause damage.
Contrary to what a lot of people believe, it IS safe to look at a total eclipse, but only for those seconds or minutes when it’s total. But it’s really tempting to look at it especially in the few minutes before it’s total, and you may not realize the danger.