whatever gets you here

a macguffin is a plot device - something to create a plot in a story - that, itself, is left very vague or unimportant. in the words of legendary filmmaker alfred hitchcock (the word's de facto founder):

"in a thriller the MacGuffin is usually 'the necklace'; in a spy story it is 'the papers'"

it doesnt matter that the theives are planning a heist for the necklace. it could be a painting or a stash of gold - but this macguffin's importance sets the scene for every character's intentions.

recentism alert! go see avatar. there is a human/alien conflict because the humans want to mine the mineral unobtainium, a valuable substance, from the alien homeworld. the audience does not care about the details of this mineral, the only important thing is the struggle to get it.