Motions can be inclusive or exclusive. It works like the different ways of annotating ranges: [0,1] and (0,1).
Consider the command `d` (delete) combined with the motions for `"`.
First we have `da"`, it deletes the everything between the pair of `"` characters that surround my cursor. Next, `di"` deletes the contents of the `"` pair.
The movement `a"` is inclusive (think 'a quote') and `i"` is exclusive (think 'inside quote'). Combined with the command you get "delete a quote" and "delete inside quote" when the mnemonics are spelled out.