A practicing geologist can benefit from the history of geology professionally in two main ways: by learning about past mistakes so as not to repeat them and by finding out about different ways to discovery. In this article, I discuss some aspects of the history of stratigraphy and point out that the concept of a stratum has shoehorned geologists into thinking time and rock equivalent, which has led to some serious misinterpretations of geological phenomena, such as the timing of orogenic events and the charting of sea level changes. I call this the "tyranny of strata." The very name of stratigraphy comes from strata, but what it does is simply deduce temporal relations from spatial relations of rock bodies, including fossils, by making certain assumptions about processes, that is, invoking inevitably a hypothetical step. What we have learned from looking at the history of geology is that empirical stratal correlation, even when well controlled by index fossils, can never yield perfect temporal correlation, and any assumption that it does is doomed to failure. Geology progresses in a direction that it may soon be possible to date every package of rock in a way to know what process is being dated and where exactly. We can correlate only processes in time hypothetically, not rock bodies empirically. This is the most important lesson a stratigrapher ought to have learned from the history of his or her subject. For such lessons to be usable by professional geologists, they must be narrated by those who are familiar with geological practice as scientists.