Lots of good answers which add a lot more value than mine. I'd like to answer it with an xkcd comic - https://xkcd.com/1425/ https://xkcd.com/1425/ that hopeful

Lots of good answers which add a lot more value than mine. I'd like to answer it with an xkcd comic - https://xkcd.com/1425/ https://xkcd.com/1425/ that hopefully gets the message across as to why we estimate.