In bodybuilding, it is known that you should always work your weakest muscle first. If your biceps are weak but your triceps are strong, always working your triceps first will leave you little energy to work and build your biceps -- your biceps will remain weak.
Similarly, when advancing our knowledge and intelligence it would make most sense to concentrate on those things which we find most difficult -- doing so would insure we live to our highest potential and do not become highly limited in our abilities.
Believing we have limits, and doubting the possibility of that which we cannot even imagine, greatly limits the extent to what we can accomplish. After all, believing something is possible is the first step in making it a reality. Christopher Columbus sailed across the ocean, Thomas Edison created the light bulb, and the Wright Brothers successfully proved manned flight was possible, by having strong belief in their possibility.
As human beings, we not only have the unique ability to make conscious decisions, but to take something unbelievable and believe it is possible. This leads us to discovery, invention, learning, and the self-improvement. It is our belief that we know everything which prevents us from discovering and learning new things. It is said that there are so few things left to be invented now-a-days, but I believe it's the vast wealth of information available to us that is restricting our creative energies. We're constantly reminded of how much we already know and how much we, as a human race, have learned and discovered.
Martin Cooper invented the cell phone after watching some of the first episodes of Star Trek. He saw Captain Kirk communicate wirelessly using the communicator and said, "Why not? That should be reality!". The cell phones carried around today are even more advanced than the "science fiction" communicator used in Star Trek.
Believe in possibility.