This slide shows the critical temperatures of ethanol from different measurements. From which you can find there are two groups of data, one is around 514 K, the other 516K.  Which one is more close to the true value of pure ethanol? Knowledge and experts suggest that ethanol is very difficult to separate from water. If the sample of ethanol contains water, it is very possible the measured Tc is higher than the value of pure ethanol. Experts suggest the 514 K should be the correct one.
	This example shows the importance of knowledge.
	But not only that, this example also implies the importance of inference.  Because the problem described above is also true for similar systems and for other properties. We can get more information based on that knowledge and inference.