Show or Tell

There's a little trope in storytelling known as 'informed attributes'.  It's when the story explains to the reader/viewer/listener subjective definitions of a character in the story instead of demonstrating such definitions through the storytelling.  In short, it's when the story (or a character in the story) says that the princess is arrogant or that the vagabond is hilarious, rather than showing those characters to be so through their own words and actions.

Informed attributes are almost always to be avoided by writers, and yet sometimes they are incredibly hard to resist.  The standard rule of thumb when crafting a narrative is "Show, don't tell", but it can be so much easier for the writer to just mention to the reader that the the little orphan girl is clever, rather than trying to contrive a scene to demonstrate her cleverness and hope that the reader catches the insight on their own. 

For secondary and background characters, it is sometimes unavoidable to resort to informed attributes.  In some cases, it can be necessary to simply tell the reader information about the character, and when this information is not subjective, (i.e. that they are tall, or strong, or have a booming voice), it is perfectly reasonable to add such things to a narrative description of the character in order to help the reader paint a mental portrait of them.  Even the subjective descriptions of a character are acceptable, so long as such descriptions of them are coming from another character in the story, so that it's their own opinion of that character which they are voicing, and not the iron-clad truth that it would be if it was the Narrative Voice of Absolute Fact proclaiming that the scientist was as brilliant as Einstein.

Showing or telling of a character's attributes is just another narrative land mine to be navigated as a writer stumbles his or her way through their story.  It can seem so much quicker and easier just to mention what a character is like to the reader, rather than taking time and energy away to contrive a situation where that character is shown to be how you created them.  Still, such clunky little diversions in the tale can sometimes grow into gems of their own, and you never know what you might learn about all of the characters involved, and of the writer's own perceptions of them.