The primary "you need to understand this" difference about Japan rejection, IME, is that Japanese people readily accept anything other than an explicit yes as a clear no. Your average westerner tends to be really delusional about this, and the even the ones who accept it (like the author, apparently) are still hurt when it happens. Like, this sentence:
> “I’m sick today. I can’t make the lesson. I’ll contact you later”
Is practically a cliché of a Japanese rejection. This is a country where people will show up to an obligation half-dead, and absolutely never cancel something important at the last minute. If someone flakes on you with an excuse of sickness -- particularly if they don't apologize PROFUSELY and attempt to reschedule -- just accept that it's done. Anyone who has been in the country more than a few weeks has experienced this, and you'd have to be willfully obtuse not to pick it up.
(to be clear: I don't think OP is being obtuse. I think she's venting for catharsis, which is fine.)