"It was my intention at first to bring all this together in a book whose form I pictured differently at different times [. . . ] I realized that I should never succeed [. . . ] the very nature of the investigation [. . . ] compels us to travel [. . . ] criss-cross in every direction [. . . ] The same or almost the same points were always being approached afresh from different directions"  (Wittgenstein's preface to his PI)