Desires arise in everyone, and the spiritual quest is also a desire for freedom. Without the desire there is no goal in life since we would be going moment to moment without having anything to look forward to. What is desire? It is a tendency in the mind to achieve something. Desire has three phases, first from the moment when the desire arises, second fulfilling of it and third completion of it. Once the desire is completed, the mind expands & in this feeling of expansion you feel full, satisfied. This feeling of fullness leads you happiness, you feel good, you want to be nicer to people than usual etc.
Just like bubbles arise in a wave the bubbles of desire arise in the mind. Since it is a tendency of the mind to go from one place to the other, it is not satisfied in that state of mind and wants to keep moving. Think about it, your new job, your new degree, your new love, it felt so good during the initial periods and then slowed waned away. Why does this happen, because the desire is for objects of the senses and not for the self. When you (self) become full, life becomes full and problems become challenges. The spiritual journey is to desire for that fullness.