why is the second set of data more challenging vs the first set which data sets are more difficult to interpret why are regression data sets different why is a regression performance difference why is the difference between the first and second set of data difference between first and second set why are first set performance different than second sets why the performance discrepancy between the second and first set of data is so important why does the performance difference between the first set and the second set? difference between test data and data why do regression testing and validation have performance differences what is the difference between first and second set of data why is the first set of data similar to the second why the first set is a tougher test case or worse what makes a regression performance difference what is the difference between second set and first set why are performance differences important in regression how to explain the difference between the first and second sets of data why are the test and validation data similar when compared to the second set how to explain regression performance differences