Comment by mpalmer

    How can things be compressed without losing information or structure?

Because the initial content is rarely the most efficient representation, so it's possible to store fewer bytes that can deterministically be converted into the original.

    Like for text, what would that involve?

Most compression algos don't care what information you're compressing. All they see (all they need to see) is bytes. It ends up being way more sophisticated than removing repeated periods and whitespace.

Like if you had eight boxes of loose lego, simply shuffling around the boxes wouldn't give you much in the way of reducing the space the legos take up. but if you took the legos (bytes) themselves out of the boxes, you end up saving a lot more space.