Facing a raise: how to defend

Why does the big blind defend so much wider?

Two reasons, and they stack. The big blind has already posted a full blind, so it is getting a discount to continue that no other seat gets. It also acts last before the flop, which means it closes the action and never has to worry about someone behind waking up with a hand. Cheap to call and nothing left to fear is exactly the combination that lets a seat defend wide.

The blinds guide covers this in full, including why the seat still loses money despite defending so much. See the small and big blind.

How do you actually learn these?

Not by staring at fifteen grids. The gap between recognising the right defence on a page and finding it under a clock is where the money goes, and closing it is a matter of repetition. PlusEV deals these exact spots back to you and returns to the ones you keep getting wrong. The full opening ranges these defend against are in the chart library, and the positions guide explains why seat decides so much.