The nature of the desert earth is not to give fruit. Even when it is planted, all the water and minerals it needs have to be constantly supplied for the plant not to shrivel up and die. Fertile land however, takes seeds and supplies all their needs for them to grow and give fruit. All it needs is a guiding hand to make sure that what its growing are plants and not weeds.
When people have an intuition as to what Hashem wants from them, they are probably right and should follow their intuition, but before they commit themselves completely they should put their intuition to the test of reason, and make sure their decision is truly wise. If it does stand up to the test, it is a clear indication that his intuition was a small form of prophecy called 'Ruach Hakodesh'.
When the select righteous individuals who were chosen to overcome the sorcery of Midyan decided to leave the women alive, they were acting on a true impulse, for Moshe Rabbeinu himself later said to leave the very young among them alive. Their intuition was right but hadn't been put to the test. Intuition is very valuable, but also very tricky and often wrong.
When the tribes of Gad, Reuven, and half of Menashe came to Moshe Rabbeinu and told him that they felt that the land of Og and Sichon was best suited for their spiritual growth it was like a woman telling her husband of an oath she had made and asking for his approval. Before he agreed to their request he made careful stipulations to ensure the purity of their intent, for intuition is based on the heart, and the heart is prone to confusion between good and bad.
Based on Rabbi Vali's book on Bamidbar. Questions and subscriptions can be mailed to: the Yeshiva