I constantly marvel at the fact that I’ve never hurt myself with a circular saw.
That probably sounds like I am not very cautious when using it. However, quite the opposite is true. I am always much more cautious using that than any other tool. There’s no great mystery, though. It roars to life when you squeeze the trigger and chews its way through anything it touched. It demands attention.
I have, however, seen some rather silly behaviour. One time, I was watching someone cut some plywood. He had two sawhorses set up to hold the sheets. He was about halfway through his cut when he reached underneath to see if he was cutting through.

Maybe that’s a natural thing to wonder, especially set up like he was where he wanted to cut through two sheets at once. Anyway, I yelled very loud and stopped him from removing his finger tips.
Circular saws are very very loud, so you need to yell to make people hear you.
Another time, a different guy on a different job site was cutting off 2x6s quickly. So, he was holding the wood with his left hand and using the saw with his right. Unfortunately, during one of those cuts, the saw kicked back and cut his thumb.
The cut was fairly deep but it’s not like he almost lost it. He went to the hospital and got a couple of stitches. When he went back to work the next day, he constantly held his left hand in the air. when asked, he said the doctors had told him to keep it elevated. So, he had his hand stuck up in the air for a week. Needless to say, he didn’t get very much done. But he did get a good new nickname from it – Thumb-Cutter.
His use of the saw when he cut his thumb was not anything I haven’t done. When you’re trying to get something done, you don’t always have the perfect set-up. You normally think it’s a waste of time to get or make sawhorses. Quite often, on a job site, you’re actually standing in six inches or more of mud and your main concern is that your power won’t ground fault. Nothing is more annoying than walking all the way back to the electrical panel to press the reset button on a GFI outlet only to find, when you return to your saw, that it’s already tripped it again.

Anyway, holding the material and cutting it with a circular saw is a reality on construction sites big and small. Almost every instance of someone getting cut in that situation is the result of carelessness or insufficient respect for the power of the tool.
I have seen, one many occasions, people making forms for concrete sidewalks. They reuse wooden stakes made from 2x4s and have to make them sharper before they start (When you drive a 2×4 stake into the ground, it immediately hits a stone and blunts the tip. Even if you try it in sand it happens – like magic). I’ve watched the sharpening process. Normally, there is a guy who is at least sixty years old, normally somewhere under 5 feet tall, and he has a heavy worm-drive saw. On close inspection (a casual glance), you can see that the blade guard has been removed and the blade is set at maximum depth of cut. The saw may even start when plugged in because the switch has been wired on (squeezing the trigger on those saws can cause carpal tunnel).

When you’re a kid, you build things to try to make them look a certain way. You build a doghouse to look like a doghouse. You have no real structural concerns. If you have 6 pieces of plywood, you’ll probably nail them together house-of-cards fashion and be happy with what you’ve made. The dog may be suspicious and somewhat afraid the new dwelling won’t survive next winter’s snow load, but you’ll take pride in your architectural genius.
A ladder, however, is something you use. You notice it’s not right when the rungs fall off under your feet or it’s too much a step to get to the next rung. You learn real lessons building things like ladders when you’re young and ignorant.

Why would someone have the saw set up like that? He starts with a massive pile of 2×4 stakes on one side and then, one by one, recuts the pointy end. If you have ever had need to try to recut a stake with a circular saw, you might be aware that the easiest way to cut is to start at the point. But when you cut off a small strip of something, the strip can get in the saw blade guard. Or, if you have the saw set at maximum depth, the wood can get a bit stuck if it gets between the guard and the saw. Anyway, there are plenty of excuses for making a dangerous tool way more dangerous, if you need to cut a lot of stakes.
And those excuses are always ok until the saw ends up cutting off your leg.

Just to note, this has been on my mind because I’ve spent this week cutting plywood on a jobsite and realized that my saw is almost 15 years old and still going strong. It hasn’t lost power and has cut miles and miles of plywood and lumber. And I think I’m just as wary of it now as when I first got it. But it’s not fear, it’s awareness. And if you limit the stupid things you do with any tool, you truly reduce the likelihood of injury.