Why I ditched measuring cups and my baking got way more reliable
I found out that every time I used a cup for flour, the amount was different. This made my cakes dense or my cookies spread too much. Using a scale solved all my consistency problems. Most bakers don't want to hear this, but cups are holding you back.
Lily's point about it changing with your mood hits on the bigger problem, which is that the person writing the recipe was probably in a mood too. So many recipes are just someone scooping from their bag, meaning their "one cup" is already wrong. A scale cuts out their guesswork and yours.
Ugh, yes, this was my exact problem with cookies. They'd always spread into one giant sheet because I was packing way too much flour into the cup. My brownies were weirdly cakey for the same reason. Once I figured out that a "cup" could be 120 grams or 150 grams depending on my mood, I bought a scale. Everything comes out right the first time now.