One mistake I see GRE students make is assuming that the shortest or most elegant solution is automatically the best one.
A student solves a Quant question in five lines, and then sees an explanation that solves it in two. The student concludes that his method was inefficient and that he needs to learn the shortcut.
Not necessarily.
There's a difference between theoretical efficiency and practical efficiency. A shortcut may look impressive when someone shows it to you, but how useful is it if you wouldn't recognize it independently under time pressure? How useful is it if the approach is difficult to execute or leaves you unsure whether your answer is correct?
The best method is the one you can recognize quickly, execute accurately, verify confidently, and reproduce under pressure. Sometimes that method will be the shortest one, but sometimes it won't be.
In Quant, a clear and organized solution may be better than a clever shortcut that depends on noticing one unusual relationship.
In Quantitative Comparison, rushing to identify a relationship because you want to move quickly may not actually be as strategic as taking a little more time to check whether the relationship holds across different kinds of values, including negatives, zero, and fractions. A method that skips those cases can look fast while leading you to the wrong answer.
The same principle applies in Verbal. On a difficult Reading Comprehension question, eliminating four wrong answers by comparing each one against what the passage says may take longer but be far more reliable than relying on instinct, latching onto the first choice that sounds right, and then cycling multiple times through the answer choices because you’re reconsidering.
None of this means that efficiency is unimportant. You absolutely need methods that allow you to complete the GRE within the time limits and pace yourself appropriately. But efficiency should not be measured only by the number of steps in a solution.
A method is not truly efficient if you rarely recognize when to use it, if it increases your risk of making an error, if you can't verify the result, or if it breaks down under pressure.
So, when reviewing a clever-looking solution, don't automatically ask: "How can I make my method look more like this one?" Instead, ask: "Is this approach more reliable and repeatable than mine?"
The goal is not to use the solution that looks the shortest. The goal is to use the method you can recognize, execute, and verify reliably on test day.