When the astronauts in Interstellar reach Mann (the planet and the ..man) they receive a disturbing message from Cooper's daughter Murphy.
She states that Dr. Brand (senior) had already 'solved' the equation he was working on to the maximum extent he could, but lacked vital data from a black hole in order to complete it. Since they had no way to get the data, the entire 'Plan A' is a sham and there is no way to save the people remaining on Earth.
As they are reeling from this news and from Murph's (incorrect) accusation that Coop and Dr Brand (junior) knew before departure, Mann further surprises them by admitting that he knew all along.
Given Mann's later actions, ..no scratch that, given the possibility of how that knowledge might make him behave, why was he given information that was deemed too dangerous to give to the later crew?
I'm thinking it should have been plausible to advise all the 'first mission' volunteers that even if their planet was not suitable, no problem, put themselves into deep sleep (or whatever they called the suspended animation chambers) and we'd drop by and pick them up once we'd become established on a suitable planet.
I can't really understand why anyone that left Earth needed the information, so why give it to Mann?