Leaders face certainty and uncertainty when painting their vision – e.g., revenue must cover expenses for an organization to be viable, but the timing of each must be in relative balance or problems will overtake any chance of success.
That there is no crystal ball to give a glimpse of certainty to the planning process does not stymie a good leader – do the thinking and research, be clear on the mission and goals, map a path to achieve success, and turn folks loose to achieve it.
It's a myth - a misunderstanding – that once the leader shares a vision, plan, mission, or goal that these are cast in stone and unamendable.
Just not true – if the element is not viable, it is wise to 'fail fast' and replace it with a better approach; if the element is falling short of what's expected, amending it for improved performance is imperative.
Results are important, protecting ego by holding course is not, and churning (making too many changes) creates a zig zag path of wasted resources. Putting in the planning up front pays dividends to the success of the mission.
The Constitution of the United States epitomizes this approach – the Founding Fathers have created a governance structure that has endured – it's in its 227th year now, and the Constitution has been amended only 27 times during that period.
Ben Franklin's quote above is actually expressing his opinion about how the Constitution will fare in the future – here's the complete quote: Our Constitution is in actual operation. Everything appears to promise that it will last. But in this world nothing is certain but death and taxes.
Appears that Mr. Franklin was correct in his assessment, so far anyway.