Exactly. In terms of word and sentence stress, Italian and English function in the same way. The unstressed syllables are hard to hear relative to the stressed syllables, but it’s the pattern of the stressed syllables in an utterance, and the context, that makes is understandable (and efficient.)

That first syllable – the one you didn’t hear – is just the one vowel with no consonants before or after, and is anyway unstressed because the stressed syllable comes later. So it’ll be more or less impossible to hear distinctly in normal (connected) speech. As you say, context helps with listening, but always, not just for native speakers. One of the reasons to do lots of listening practice is exactly that – to get the brain’s alogorithms used to doing what they do already in your native tongue, and other languages you knoww well, but with the new language. Once people start listening regularly, it almost always comes together quite quickly, and understanding the spoken language ceases to be a problem.