What is the hardest wine to drink?

I'm curious, what do you consider to be the hardest wine to drink? Is it a particular type of grape, perhaps a bold and tannic red like Cabernet Sauvignon? Or could it be a sweet, fortified wine like Port or Sherry that might be too intense for some palates? Alternatively, is it a matter of personal preference, where certain individuals find certain wines difficult to enjoy due to their unique flavor profiles or alcohol content? I'd love to hear your thoughts on this intriguing question.