That is so true. It is also something I completely failed to get across to my learners in the nine months I worked in China.
I tried working with them on such patterns as bat/mat/sat, bad/mad/sad, bet/met. It seemed to make no difference. Even after I had pointed out the underlying system, they would insist that they had no idea how to pronounce, for example, set when they met it for the first time.

Student or Learner