The most common mistake in baking is mismeasuring, and it happens to novices and professionals alike. To build baking confidence, know that your measuring tools are accurate.
Many people find it surprising that you can’t assume accuracy in volume measuring tools (dry measuring cups, liquid measuring cups, and measuring spoons), but I’ve fallen victim to this myself, having discovered that some of my favourite sets are not truly accurate. A supposed 1-tablespoon (15 mL) measure that is actually ¼ teaspoon (1 mL) less or more may not seem like a big deal, but it can greatly impact a recipe, especially with ingredients like baking powder and salt.