Do you understand almost everything people say on TV?

I get the impression that people, when speaking English, mumble a lot or squash their pronunciations with too strong accent or talk too fast… I’m listening with a foreign ear. I don’t speak English as a native. So please muster up all your memory and think back hard. Of course, it isn’t natural that you can’t understand 100% because it’s your mother tongue after all. Nonetheless, I couldn’t help asking this because I do get that impression.
So sometimes I don’t understand words which would have been perfectly intelligible in writing.
For instance, watching a Korean movie, I often miss some words. For some movies, If I don’t turn up the volume pretty much, I can’t even grasp the story line. Does this happen a lot to you guys too?