the task of the professional philosopher is critically to investigate the things that so many others accept as evident. In fact, quite a lot of such opinions are mere prejudices, uncritically accepted as evident by very often simply false. And to get away from them, perhaps something like a professional philosopher is required, who will take his time to reflect on them critically.which is from pages 8-9 of Offene Gesellschaft, offenes Universum, Franz Deuticke, Vienna, 1982
So whenever someone says an idea is too obvious for critical debate, too evident to take seriously disagreement about it, too well established to doubt ... well, that's silly. As Popper points out, people take for granted many false ideas, so the fact that it seems really obvious to you is no guide to its truth.