I am a parent, and I told my son no about a great many things when he was young. He heard yes often enough, but he learned that he didn't get everything he wanted when he wanted it. The reasons that he heard no don't really matter. We have never been arbitrary parents that said no for no reason, but we have said no and not given an explanation. I think that works well for children. They do deserve explanations about some things, but other things they simply need to hear no and that is that.
While I'm on the topic, there are a fair number of adults that need to hear this word. I know some adults that get everything they want and never hear no. I think it's time that someone said it to them. Life does not revolve around any one person (and certainly not me). We all need to hear no once in a while so that when we hear yes, it actually means something.