While the two terms are often used interchangeably, there is actually an important, highly under-appreciated difference between being “efficient” and being “effective”. And this is perhaps more true in foreign language learning than any other endeavor!
Timothy Ferriss, author of The 4-Hour Workweek and a very accomplished language learner to boot, illustrates this point well:
“Effectiveness is doing the things that get you closer to your goals. Efficiency is performing a given task (whether important or not) in the most economical manner possible. Being efficient without regard to effectiveness is the default mode of the universe.”