Many of the great challenges of our day have not been done because they are difficult. Land humans on Mars. Build a car people want that gets 100 miles per gallon on gasoline. Run the Appalachian trail in less than a month. Climb two 8000 meter peaks in one day without bottled oxygen. A smart watch with battery life for three days. There are many other challenges.
The point is, we have already done the easy things, only the hard things are left. One might say that it has always been that way. It is always hardest being first to do something, whether it is the iPhone or the four minute mile. The challenges that are left are seemingly even harder than the challenges that have been done.
I ran the numbers on a "project" a couple nights ago, and the reason no one has done my project is that using current technology, it is not possible. It was humbling to look at the raw numbers and understand that the solution to the problem would be far more intricate and detailed and non-obvious than I was hoping.
I guess that just means that accomplishing these goals we have will be that much more significant.