This sounds really dumb but can a tampon break your hymen?

That myth is why mothers around the world refuse to allow their daughters to use tampons.

myth fact has been around for over 60 years

https://www.youtube.com/watch?v=9qFojO8WkpA

In theory it can. It mostly won't... the hymen is a thin flexible bit of tissue that runs around the bottom entrance to your vagina (admittedly, mostly. Some women have variations).

The great bulk of women can put things like tampons into their vagina and cause absolutely no issues to their hymen at all.

Not likely. Not unless you are being aggressive and forcing the tampon. If you go gently, it will not puncture anything.

It mostly won't the hymen is a thin flexible bit of tissue that runs around the bottom entrance to your vagina (admittedly, mostly.

No - it can not. The hymen isn't a mass of solid tissue. It's band of tissue that lies along both sides of the vagina. It doesn't break - it stretches. It has an opening in it, through which something no larger than a tampon can easily pass. If it didn't have an opening, you would be unable to menstruate.

Possibly, but you already have an opening in it (how else would you have periods?) so it would depend how large that was, more likely it may stretch it further