You can’t understand English fast – or you can, but not if your ‘English’ is bad.
The point here is that there is no such thing as ‘speed of understanding’. If you understand an English sentence, then you understand it and the time it takes to do so doesn’t matter. The question of whether you understood it in one second or five seconds or ten seconds makes no sense: if you did, then you did and that’s all there is to it. Of course, some people may understand some sentences faster than others, but this has nothing to do with speed: it’s just a difference in familiarity and/or exposure to the structures concerned (which may be related). And your exposure will vary depending on how much and what kind of English you read and listen to and so on.
Secondly, it’s important to distinguish between:
* speed as a feature (the time taken to utter some sentences)
* speed as a quality (how quickly you can move your hand)
When we use the word ‘speed’ in a first way, we’re often really talking about fluency: just because somebody speaks Italian doesn’t mean they’re fluent and it’s the same with English. Fluency is what gives us confidence and makes us sound natural, but nobody speaks perfectly fluently all of the time. If you listen closely, even native speakers ‘back off’ from certain words or structures because they realize they don’t need them which means they might not be fully fluent when they say them.
And if you speak a language fluently, it doesn’t necessarily mean you understand it well: in a very broad sense of ‘understanding’, we could say native speakers understand their own language perfectly but that doesn’t mean they always know the etymology of words or can tell us when something was invented or how idioms work. Again, this is why fluency and understanding are different things. Or rather, fluency is often a component of your overall understanding because somebody is more likely to use structures correctly if they’re familiar with them anyway (which makes sense since communication requires both partners to make each other feel understood). This may sound complicated but actually it that using them correctly would take too long – so yes, speaking fast usually means speaking fluently! But this isn’t always true: people speak very quickly without making many mistakes and this is a sign of a high degree of fluency.
It’s the same with understanding: being caught out by an idiom or figure of speech usually means you didn’t fully understand everything that went before it. So if you take your time, you’ll often find there were more elements to what someone said than you’d realized initially. Fluency is great for getting your message across but sometimes we need to slow down in order to get our ideas straight. And I’m not suggesting that everyone should speak slowly all the time because that wouldn’t be natural either – just as nobody speaks perfect Italian all the time! However, there are times when a slower approach will help us produce a more coherent sentence structure and avoid those ‘um’s and ‘er’s!
This is why the idea that fluency means speaking faster is misleading. Fluency isn’t related to speed at all – it’s related to what you can do with the language, sometimes regardless of how long it takes you to say things. If English is your first language, for example, you can probably understand most spoken English pretty quickly provided people aren’t talking too fast or mumbling (even then they shouldn’t be hard to make out). Our brains are extremely good at processing speech because we speak our own languages so well! However, if listening isn’t your strong point, then slowing down might help you work out some words/structures more easily by giving yourself time to think about them without being under pressure. And if you speak another language, then you may need to slow down in order to process the information at all. To be fluent in a language requires us to understand that language fluently but this doesn’t mean we should always rush through what we’re trying to say!
So don’t feel disheartened if you’re concentrating hard on understanding others or saying things correctly because it’s great practice for any learner of English (or their native tongue ‘L1’ if they speak more than one). Fluency is very much related to how you use English not just how fast/slowly you speak it so keep practicing both your speaking and listening skills. The better they are, the more fluent you’ll sound!