Problem Solving and Cognitive Principles

Below is a list of numbers. Can you figure out the sequential pattern?

18, 11, 15, 14, 17, 16, 13, 20

To solve this puzzle, most people focus on the relationship between each number, and thus find it challenging to solve. To discover the pattern, you must not consider the value of the numbers themselves, but rather the fact that the numbers are in alphabetical order. Did your focus on the numerical relationship prevent you from seeing the solution? Why do you think this happens?