The grammatical function words in a sentence are usually unstressed and so sound different to how you might expect. Can you recognise the word - you - when it's pronounced in it's weak unstressed form?
Can you recognise the little grammatical function word - OF - in spoken English? OF is often hard to hear and sounds very different to how you might expect, especially when the word after _of_ begins with a vowel sound.
In everyday spoken English many words are pronounced in their weak form and don't sound the way you expect them to sound. The grammatical function words are usually unstressed and so are pronounced in a weak form and the vowel sounds are often replaced by the shwa sound.
The little grammatical function words are often very hard to hear. These words often sound different to how you might expect them to sound. This video is about the word CAN.