Alice Schertle and Jill McElmurry’s picture book series featuring Little Blue Truck has sold, as the website says, more than “20 million books.” I decided to pick one up to see what all the fuss was about.

I picked up the first my library had available, which was a board book version of Little Blue Truck. In many ways, this is a classic version of a picture book (even a cliched or stereotyped version). This classic feel starts with the title, which shrinks the focus: one truck, and a little one.

The story is told in verse: rhyming quatrains with very short lines. The rhyme is regular; the rhythm shifts around a bit. For example, the first two lines are four syllables each; the third is three syllables, the fourth five syllables.

There are lots of animals here, and lots of familiar sounds, with a useful counterpoint and interaction between the animals and the truck: the truck beeps and the animals croak, or the animals moo and oink, and the truck beeps.

There is a plot and a lesson, both focused and simple: a big yellow dump truck muscles past Little Blue Truck, too busy to slow down and talk to the animals–and immediately gets stuck in the mud. He calls for help, but no one comes to help. Little Blue Truck catches up to him and tries to help–but gets stuck too. However–and here’s the lesson and the plot twist–when Little Blue Truck calls for help, the animals he’d been friendly with earlier show up, pitch in, and get both trucks out of the muck.

The dump truck realizes the error of his ways, driving the lesson home–and then Little Blue Truck rewards his animal friends with a ride.

Alice Schertle’s book came out in 2008, but really, it could have been published 50, 75, or even 100 years earlier: nothing anchors this to the present except maybe the models of the two trucks. The same is true for Jill McElmurry’s illustrations; they are warm, gently stylized, and gently anthropomorphized. (Little Blue Truck’s headlights are eyes, for example.)

This is good, but I almost feel like it has sold so much because it is so easy, obvious, and familiar to the adults reading it.