Something is efficient if it performs optimally under ideal circumstances.
Something is robust if it performs pretty well under less than ideal circumstances.
Life is full of trade-offs between efficiency and robustness. Over time, I’ve come to place more weight on the robustness side of the trade-off. I imagine that’s typical. With more experience, you become more willing to concede that you haven’t thought of everything that could happen. After a while, you notice that events with a “one in a million” chance of occurring happen much more often than predicted.
Robust things are often more efficient than efficient things are robust. That is, robust strategies often do fairly well under ideal circumstances. You may not give up much efficiency for robustness. But efficient strategies can fail spectacularly when the assumptions they’re based on don’t hold.
Related post: Six-sigma events