One of the texts that made things click/unclick for me was Simone de Beauvoir, Second Sex. Just the first few paragraphs of the introduction made me rethink a lot of things.

De Beauvoir asks, what is a woman? When you realise most of the ways that women have been defined in (white, bourgeois) patriarchal society are inconsistent and contradictory, the 'traditional' view of women starts to unravel. De Beauvoir hands you a strand of the old woollen jumper of gender; if you pull it, the jumper falls apart.