One of the most common mistakes made by new bakers is not measuring ingredients properly. Yes, measuring is actually a skill!
Measuring mistakes typically occur when measuring by volume, meaning using measuring cups instead of a scale. This method of measuring uses the amount of space an ingredient takes up as the measurement, instead of how much it weighs. It is very common for this to be inaccurate, depending on a variety of factors.
For instance, flour provides the main structure for most baked goods. Flour is also a powdery dry ingredient that is very easy to pack into a measuring cup. If you ask five people to measure out a cup of flour and then weigh each of them, you will likely have five different weights. Packing down the flour, not leveling properly, and scooping the flour with the measuring cup instead of spooning it into the cup, can all affect how much flour takes up a given amount of space. Additionally, not all measuring cups are completely accurate in size. This can cause many issues with your baked goods.