I am reminded of how many "air tight" (excuse the pun) cases have been brought in California (ok, its California) only to have the defendant found not guilty. Right off hand, I recall O.J. #1 (murder charge), Michael Jackson (child molestation charge), Robert Blake (murder charge) and Mike Corona (corruption). In addition, if my recollection serves me, the big gang rape trial in Orange County resulted in a hung jury despite the fact the whole thing was caught on video tape (on the second trial, there was a conviction. There was a hung jury in the first Phil Spector trial.
So, saying that the prosecutor would not bring a case unless it was a sure winner means very little.
OTOH: since jurors often think the same way, it is real bad to be a criminal defendant. That mindset is the first strike. The second strike is that most criminal defendants who sit there in court expect to be convicted (they know they are guilty) and as a result give off an aura of guilt, which the jury picks up on.