Scientists must be able to enjoy the process, the greasing of the pan and the digging out of the eggshells, and not live solely for the result. In the case of cooking, the cake is guaranteed within a short period. Not so with science. Every scientist finds her compensation in a slightly different manner. One researcher I work with likes the inexactness of biology, the fact that the simplest explanation is never the correct one.
Science is an adventure, albeit a personal one for the most part.
The complexity of biology is incredible, and the anticipation generated by trying to solve such an intricate puzzle can be addictive. Other researchers in my lab are more methodical. Carefully performing every experiment with all the appropriate controls every time gives them a deep satisfaction. Showing a perfect gel with crisp, clear bands at lab meeting, whether or not the answer was the predicted answer, is the essence. Scientists never get their whole reward at once.