Calling other functions from a shared (or static) function

Question

I get this error: Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.

Partial Class _Default
    Inherits System.Web.UI.Page

    <WebMethod()> _
    Public Shared Function ParseData() As String
        Dim value as string = GetValue()
    End Function

    Private Function GetValue() as String
        Return "halp"
    End Function
End Class

I know it has something to do with the fact that the first function is shared and the second function should probably be Public as well but I don't fully understand the reason behind it. Probably not relevant but I'm calling the web method from some javascript.