It doesn't give you all the information you need, but that's how the problem was originally tackled. Scientists noticed that they had two contradictory models for light, which had a few overlapping characteristics. Those overlapping areas allowed them to start formulating new theories. Of course it took ridiculous amounts of work after that to figure out a reasonable approximation of reality, but one has to start somewhere.
Happy New Year! Here's the latest and greatest installment of rationality quotes. Remember: