This summary is not the rule. The rule text controls.
Lawyers can't file lawsuits or raise legal arguments just to waste time or harass someone. Before bringing a case to court, or fighting one, a lawyer needs a real basis in the facts and the law. This doesn't mean the lawyer has to be certain they'll win. They can make good faith arguments to change existing law, challenge a law they think is wrong, or push for a new legal interpretation, as long as the argument is genuine and not just noise.
There's an important exception for criminal cases. If someone is charged with a crime, or faces a situation where they could go to jail, their lawyer can make the prosecution prove every single part of its case. This is true even if there's no real dispute about what happened. The government still has to do its job and prove guilt, and the defense lawyer isn't acting improperly by holding them to that standard.
In short, this rule stops lawyers from filing bogus claims or defenses just to cause trouble, while still protecting a person's right to make the government prove its case in criminal matters.