I don't think it's a matter of actually believing something is impossible, and being arrogant in stating it. That's oversimplifying matters.
What most people mean when they say something is impossible, is either that they can't muster the necessary will to do it, or aren't willing to make the attempt.
It's like losing weight - we all know what it takes to lose weight, or get fit, we all know we can do it, so when we state it's impossible, what we are saying is that we aren't willing to put in the work. We don't want it bad enough, in other words.
I do HEMA (historical fencing), and from time to time I think to myself "damn, it would be great if I was good enough to enter the big tournaments, but that's impossible". I know it isn't impossible, of course it isn't, it's just a thought. It isn't even that anything is holding me back, it's that I'm not willing to invest the time and effort necessary to achieve it. I don't want it enough, or I want other things more.
In the case of losing weight, it's a matter of enjoying food more than you enjoy being fit - not because people truly believe it's impossible.
But that's just my two cents.
I agree with you, but you are fully aware that it would be possible do get into big tournaments and that you want to spend time and energy in other activities, which is great because to get the best of what we can from life you need to say no to a lot of things to make space for what you enjoy the most.
The problems is that many others truly believe they aren't capable at all, that they wouldn't be capable of even if they tried, they use different reasons to justify.
Example of reasons to justify:
The post wasn't a criticism to people that say that in general, I say that all the time. As you say we use it in a general way to say that we don't want it enough. My point was to question the moments when we say that about the things we truly want and would be willing to put the time and effort to achieve if we at least believed that it was possible. Sometimes we don't truly think about that, we over simplify because we don't find a clear or simple enough path and just accept it can't be done.
Thanks for your contribution, I truly appreciate it.
I do like your point that we don't think about it sometimes. It could very well be a destructive line of reasoning, assuming something is impossible. Say something is impossible enough times, and you might end up believing it actually is.
I think it's never a bad thing to stop and think about how we use language, and your post touches upon that. Perhaps people should refraing from saying something is impossible, and instead consider if that's truly the case, or if they just don't really want it all that much.
Cheers, have a nice day mate!