If you ask a baker what protein does in dough, they'll tell you protein forms gluten, the stretchy web that's necessary for making bread (but a less desirable quality in things like cakes). Protein affects the amount of water that flour can absorb. It's thirsty. Dough made with high gluten flour will seem less wet than dough made from flour with a lower gluten content. This can be true even if the same brand of flour is used to make the same dough. While measuring errors are one common problem, even if the measuring is precise, doughs made from the same recipe can feel different. The reason being, protein levels can vary within the same brand of flour. Although brands state the percent of protein on the bag, the numbers fall within a range depending on the manufacturer's tolerances. The true percentages can be significantly different enough to produce very different outcomes. But how much difference does it make?