Ben Silbermann, the chief executive of Pinterest, “measures twice, cuts once,” said one early investor in the company. : SAN FRANCISCO — Ben Silbermann does not enjoy being interviewed. He isn’t a fan of speaking at tech industry conferences. Nor does he like sitting for glossy magazine portraits. He doesn’t think he should have to explain Pinterest, the web service that allows people to save images to virtual pinboards, to anyone other than those who want to use it.