Answer:
If you change everything at once, you may not know what caused the end result.
Step-by-step explanation:
If you have Variable A (Salt), Variable B (Potassium), and the Control of Water, you might mix everything together, so you mix salt, potassium and water together. It is known that Potassium reacts very aggressively in water, but since you mixed everything together, you might think that salt+potassium+water goes boom, while it is actually potassium+water=boom.