Think of it this way: Before we make a telephone call, we need to know whom we are calling and we need to be confident that the person really exists and will be receptive to our call.
Ibaratnya begini: Sebelum menelepon, kita perlu tahu siapa yang akan kita hubungi dan perlu yakin bahwa orang itu benar - benar ada dan mau menerima panggilan kita.