I expect "obviousness" is mostly driven by background here. You know, e.g., that ceil(x) = -floor(-x) for any real x, and the application to integer division is just a special case of that. I expect programmers mostly don't know that, though. And Python having floor integer division is unusual among programming languages. Everyone coming from, say, C, has seen the (i + j - 1)/j "idiom" over and over, where "the usual" truncating integer division is the rule (and they know too that `i` and `j` are positive). Familiarity breeds "obviousness" too :-)