Why can I access any private within same class?

Module Module1
    Sub Main()
        Dim oMyTest As New MyTest

        oMyTest.CreateMyName("Call From OutSide, Why Can't I assign directly to MyName")
       'oMyTest.MyName = ("Why Can’t I DO THIS")
    End Sub

End Module

Public Class MyTest

    Private MyName As String

    Public Sub CreateMyName(ByVal sString As String)
        MyName = sString
        Console.WriteLine(MyName)

        Dim oMyTest As New MyTest

       ' oMyTest.MyName = "Why does this work"
' why does this work 
' if I initiate a the same class object inside the same class i can access all private fields, function, and methods.
        Console.WriteLine(MyName)
        Console.WriteLine("Inside Obect: " & oMyTest.MyName)
    End Sub
End Class