Why is Cobra not reading my configuration file?

The documentation in Cobra and Viper are confusing me. I did cobra init fooproject and then inside the project dir I did cobra add bar. I have a PersistentFlag that is named foo and here is the init function from the root command.

func Execute() {
    if err := RootCmd.Execute(); err != nil {
        fmt.Println(err)
        os.Exit(-1)
    }

    fmt.Println(cfgFile)
    fmt.Println("fooString is: ", fooString)
}


func init() {
    cobra.OnInitialize(initConfig)

    // Here you will define your flags and configuration settings.
    // Cobra supports Persistent Flags, which, if defined here,
    // will be global for your application.

    RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.fooproject.yaml)")
    RootCmd.PersistentFlags().StringVar(&fooString, "foo", "", "loaded from config")

    viper.BindPFlag("foo", RootCmd.PersistentFlags().Lookup("foo"))
    // Cobra also supports local flags, which will only run
    // when this action is called directly.
    RootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
}

My configuration file looks like this...

---
foo: aFooString

And when I call go run main.go I see this...

A longer description that spans multiple lines and likely contains
examples and usage of using your application. For example:

Cobra is a CLI library for Go that empowers applications.
This application is a tool to generate the needed files
to quickly create a Cobra application.

Usage:
  fooproject [command]

Available Commands:
  bar         A brief description of your command
  help        Help about any command

Flags:
      --config string   config file (default is $HOME/.fooproject.yaml)
      --foo string      loaded from config
  -h, --help            help for fooproject
  -t, --toggle          Help message for toggle

Use "fooproject [command] --help" for more information about a command.

fooString is:

When I call go run main.go bar I see this...

Using config file: my/gopath/github.com/user/fooproject/.fooproject.yaml
bar called

fooString is:

So it is using the configuration file, but neither one of them seems to be reading it. Maybe I am misunderstanding the way that Cobra and Viper work. Any ideas?

To combine spf13/cobra and spf13/viper, first define the flag with Cobra:

RootCmd.PersistentFlags().StringP("foo", "", "loaded from config")

Bind it with Viper:

viper.BindPFlag("foo", RootCmd.PersistentFlags().Lookup("foo"))

And get the variable via the Viper's method:

fmt.Println("fooString is: ", viper.GetString("foo"))