That is such an unhelpful mantra to keep repeating. It's phrased negatively and offers no enlightenment other than acknowledgement of your ignorance.

People qualify as worthy leaders by showing wisdom. Plenty of stuff is not super original (Facebook wasn't the first social network). Prior experience is a great teacher.

Good leaders make plans and manage their risks. Even if they are moving into a new field, they can draw on the skills and experiences of others. Then they prioritise what's important and allocate resources based off that.

As the plans get executed, they monitor progress and adapt accordingly.

There are always uncertainties. If they eventuate, the impact can be good or bad. Planning ahead means assessing the likelihoods and making appropriate contingencies.

Just acting confident is not showing leadership.