I agree. I would also say that in cases where the abstraction doesn't make sense you have to know what's going on inside the box in order to trust it. Recently

I agree. I would also say that in cases where the abstraction doesn't make sense you have to know what's going on inside the box in order to trust it. Recently at my day job, I came across a string trim() function, which started with this comment: // removes leading and trailing whitespace. Also removes commas. The code itself also removed single trailing periods. That really hurts your trust in the code base - you need to read everything a function calls to understand it, you can't trust the method names. This makes it take longer to understand any particular piece of code - even if in the end the methods called actually do what they claim to.