Everything happens for a reason. You’ve heard the saying, right? Well, this applies to your story and characters too.
Why does the villain hate the hero?
Why is the hero guarding their heart?
Why does the child think winning the science fair will get his parents back together?
There has to be a reason for your character’s motivation. When you sat to write today, you did so with a reason, a purpose. You wanted to write a story to entertain, teach, earn money. Perfectly good reasons.
Go through your manuscript and pretend you have a four year old at your side asking, “Why?” every twelve seconds. If you don’t have an answer as to why your character is doing something then maybe it is out of character or doesn’t move the story along.
Remember, EVERYTHING happens for a reason.