Very false. Generally, the difference between a good lawyer and a bad lawyer is that the good lawyer will counsel the client about the chances of not winning the case, especially after discovery has concluded, while a bad lawyer won't.
If the the winnability of a case was apparent at the start, there wouldn't be a case as the parties would settle before a formal lawsuit was filed. This happens very frequently, especially for labor cases where the employee has documented instances of harassment.
A lot of cases that appear to be "winnable" at the beginning turn out not to be winnable based on evidence that becomes available during discovery, and a lot of cases that didn't appear to be winnable turn out to be slam dunks after discovery. Most of the landmark cases today were cases that didn't appear "winnable" at the start (see, e.g., the DuPont and Erin Brokovich cases).
Moreover, for most cases of this type (and generally for almost all civil cases involving individual torts), lawyers work on a contingency basis for plaintiffs, so they only get paid if they win. The only lawyers that won't handle civil torts for individual clients on a contingency basis are the bad ones who don't expect to win, or the truly amazing ones that charge fixed or hourly fees because they're so good that they can resolve the case without doing the amount of work that would justify a 30% or 40% fee.