At grave risk of sounding even more patronizing than I usually do, let me try to help you with something:
HN people spend a lot of time arguing with each other, often about nonsense or trivia (hey, myself included). In those arguments, it is very normal to say "I have trouble believing X is true" or "I have a hard time believing Y". And while it's not the most polite way to express disagreement, it's more annoying than rude. (It is in fact a cardinal example of what my spouse Erin would say makes disagreeing with me annoying).
It is on the other hand incredibly rude to respond to someone who just made a categorical statement about something material ("We did not have a buyer from the beginning of the sale of Sortfolio", for instance) with the words "I have trouble believing you". Unbelievably rude. I think it might even be more rude than directly saying "I think you're a liar", since it's so recklessly casual.
Noticing this, I quickly searched over my old comments, horrified that I might have made the same error, perhaps even repeatedly. It is the kind of obnoxiousness to which I am prone. I am very relieved that I was not quickly able to come up with a comment here where I casually called someone else a liar.
