If it is less efficient, then I can continue programming the same way as before. I'd like to see this knee-jerk response discredited once and for all. Optimizing code is comparatively easy. Everyone claims to know how to do it. Everyone also knows how to make code unreadable and unmaintainable.
Good design is genuinely hard.
We never come close to an optimum design. After a month, any design begins to show flaws. I recommend everyone concentrate on design first and save the easier optimization for later. Really inefficient designs will be obvious, and you won't have to remind yourself to avoid them. Anyway, most optimization is local.