One thing every well we drill has in common is that the bit must get to the bottom of the hole. Some formations drill faster than you can clean the hole. Others, not so much. No bit is designed for every formation. Sometimes, most of the hole is one formation, but with streaks of a different formation the bit is not designed for. You know you have to get through it, but the bit does not cooperate. Reading the signs that the bit sends you becomes crucial to telling what you are drilling in, and how to treat the bit.
For example, on the Texas Gulf Coast, most aquifers are cemented sand with a gumbo of clays above it. Drilling there, we usually ran wing bits and very little in the way of mud additives. The clays would quickly build viscosity. Feedback from our bits told us we had to pump off often and use thinners to thin the mud.