But on top of that, the wood they break is ALWAYS endsawn, and many times it's pre-dried in an oven to make it more brittle.
Maybe where you were, were I was it was standard lumber and you could really hurt yourself if you hit any of the knots in the wood.
Since yes I've had to use wood with knots in it even in competition...
FYI you will likely never break boards that isn't cut "end grain", or if it is and hit against the grain.
There is a reason humans have made structures out of it for 1000's of years.