It's pronounced "Sen".

Judith Butler, “Performative Acts and Gender Constitution: An Essay in Phenomenology and Feminist Theory”

In other words- society ostracizes you unless you become complicit in perpetuating the erroneous assumption that gender roles are rooted inherently somewhere in your biology.

People like it when your behavior is consistent with their expectations, because that and only that will prove to them that your behavior is true, rather than some flawed disguise. (For example, a typical jock with a desire to dance ballet seems ironic or “wrong” to many people, and rather than admit that perhaps there is a sort of man who can like both football and ballet, people are much more likely to instead assume that one or the other is a “fake” identity.)

To claim that someone is “not acting like a real man” implies that you know what a real man acts like. But any attempt to point to any group of men and say “see, they act like this, therefore this is the definition of masculinity” remains completely unfounded—because from just looking at these men, you cannot read their minds. You have no actual way to determine how many are genuinely behaving that way, and how many are behaving that way in order to match the standards of masculinity that other men/society has presented to them. The “proof” you are basing your standards on may just as well be fake, or heavily influenced by pre-existing standards—standards that you are now upholding.