Well it is pretty self-evident that non-leaky abstractions don't exist -- or I haven't really seen one in all these years. Take functions in functional programming: if tail recursion matters that is one leak; if strict or lazy evaluation matters that is another leak; if you want to share intermediate results well that springs a big leak; etc. Engineering is about trade-offs. We are there to judge what matters to us and therefore "leaks" and abstract away details that may not matter to us (at the level we are working on). Yes fundamentally I do see this as the barrier to complete automation.