Sometimes learning is unlearning
The better we learn a thing, the harder it can be to unlearn it temporarily. Did you ever drive somewhere familiar-say, home after work-planning to run an errand on the way, only to realize too late that you missed the turn for the errand? Your brain has learned the route home so well that it operates on a kind of auto-pilot, requiring you to think consciously about changing your route. Essentially, you have to "unlearn" the route home long enough to make the detour.
A simple demonstration of this concept is the Stroop Test, below. Look at the words and name the color of each word, rather than what the letters spell. You might find yourself slipping up as your brain tries to take the familiar route to reading the word.