In the Feynman lectures, it is mentioned that [Vol 1; Gravitation]:

Galileo discovered a very remarkable fact about motion, which was essential for understanding these laws. That is the principle of inertia—if something is moving, with nothing touching it and completely undisturbed, it will go on forever, coasting at a uniform speed in a straight line. (Why does it keep on coasting? We do not know, but that is the way it is.)

How Gallileo discovered the law of inertia ? In those time, there were probably no frictionless area so that he could test his hypothesis. And uncontrolled "thought experiment" can lead you astray like Aristotle (who belived that continuous force is required to get a particle moving all the time).

Here, I do find Feynman's quotation (of Tycho Brahe's "idea" ) relevant, but I can't make the connection:

This [debates about the nature of the motions of the planets would best be resolved if the actual positions of the planets in the sky were measured sufficiently accurately] was a tremendous idea—that to find something out, it is better to perform some careful experiments than to carry on deep philosophical arguments.