While all children are sometimes irritating, occasionally they're completely impossible. I've joked with parents that the business office next to mine has a Saturday swap meet where children are exchanged.
But troublesome behavior has meaning since when a child is unhappy they don't spontaneously speak of their distress but instead act difficult. This is why Oppositional Defiant Behavior is the most common mental health diagnosis of children.
When asked to do something by their parent a child will usually comply since they want to grow up, to be an adult. Resistance thus indicates their inability to do what is asked because of illness, exhaustion, emotional upset, or an unspoken reason making sense to them but isn't logical. Then, speaking with the child is more productive than yelling, which should only be done when confronting a potentially dangerous or harmful situation. Otherwise, frequent yelling by a parent will cause warnings that a child should respect to be ignored.