At this stage, your child begins to understand the logical connection between ideas, which is the reason they start to ask "Why?" about almost everything. It is a big milestone in their development and comprehension of how the world works. As a part of it, they now get to live the concept of anticipation as well.
What you need to know
However, this stage can also be very confusing and exasperating for you. It’s normal for kids to seem reasonable and wise one minute and act totally irrational the next. While this is coupled with the fact that 3-year-olds are still working hard on managing their emotions, other factors will also influence how your child accepts and responds to your logical explanations. Is your child tired or hungry? Is your child anticipating something? When you tell your child that they can't have cake for lunch because their body needs healthy foods to grow strong, your child may quickly comply.
But when you tell your child that they can't go to the playground before bed, they might completely lose it. You are left confused, but that’s just how a 3-year-old processes the world. At this point it is best to explain the rule matter of factly and to be consistent in the follow through. If your child throws a tantrum, validate their unhappiness, anger, or frustration but don't relent as this will just make the tantrum a successful tool for your child.