Why is this the answer?

The answer is lie because this clever riddle uses many different ways to talk about the power and effects of not telling the truth. A lie is a statement that is not correct, and the riddle shows us all the big and small ways it can change our lives. Let's look at the first line: I'm sometimes white and always wrong. This is a fun word trick! You might hear grown ups talk about a small, harmless fib as a white lie. Even though it is called "white," this part of the riddle reminds us that a lie, no matter how small, is still "always wrong" because it is not true. Next, the riddle says: I can break a heart and hurt the strong. Think about how much it hurts when someone you trust tells you something that is not true. A lie can make people feel betrayed and very sad. Even the strongest person you know can feel very upset or hurt by a big lie. Lies can cause people to feel broken inside, which is what the riddle means by breaking a heart. The third line tells us: I can build love or tear it down. This shows that a lie can be very powerful. It might start a friendship or a relationship on something that is not real, but that foundation will be shaky. Once the truth is discovered, the lie will "tear it down," meaning it will quickly destroy the trust and good feelings you had. Trust is like the glue that holds people together, and lies can melt the glue away. Finally, the riddle ends with: I can make a smile or bring a frown. When a person is fooled by a lie, they might smile because they think something good or funny is true. But later, when they learn the real facts and realize they were tricked, their smile will quickly turn into a big frown. A lie can never bring real, lasting happiness, only a temporary good feeling that turns into sadness once the truth is known. That is why the word "lie" perfectly fits all the clever lines in this puzzle.