Totally agree — binary search is the classic example of something that feels simple until you try to implement it robustly. The off-by-one errors, incorrect mid-point updates, and forgetting to handle edge cases (like low == high) are so easy to miss.

Bentley’s anecdote is a perfect illustration of how writing "correct" code often depends more on reasoning rigor than language syntax. Loop invariants, like you mentioned, are key here — they help anchor the logic through each iteration. It’s one of those patterns that separates surface-level understanding from deep intuition.

I also like how languages like Rust (with its strong type system) or Python (with clarity) can highlight these logic gaps early, especially in interviews or algorithmic codebases.

If you’ve got the link to your example post handy, I’d love to give it a read.