Some words have two pronunciations
Having looked at stressed and unstressed syllables behave in individual words, the next step is to analyse what happens at sentence level.
Some people are surprised by this lesson, because it shows them something very different to the English they’ve learnt so far. For them it’s the introduction of a new problem. I see it differently: the fact that they were blissfully unaware of the existence of something as important as unstressed words is an indication of a solution just waiting to be learnt.