Your friend is right! Think if you were putting together a jigsaw puzzle and a whole bunch of the pieces were missing. They need to see an accurate and thorough picture of what is going on to decide how best to proceed. There can be enough trial and error as it is -- you wouldn't want to increase the chances of that by withholding info, would you?(!)
Remember too... They've heard it all, as they say. Don't worry about shocking them. Really. Think about it.
Good luck. You'll do fine!