I was in history class, and my history teacher mentioned something insightful he used a quote which i can't remember. But the basic idea was no nation would tell their story in the inferior tone but in superior tone, even if there was clear defeat against them, only to maintain they are the superior stable nation. Countries who have won their independence, consider it as a victory of separation and independence that they are, were, always, self sufficient they didn't need outside west influence. The way I see it, we wouldn't know true detail of any event, and they may be distorted to show a country is superior than the other. We can make an assumption of the result that happen. If someone can share their expertise on this, I would appreciate it. Thanks.
First, you raise the question of bias: this is one historians constantly deal with. There's a good discussion of that here, moderated by u/ThucydidesWasAwesome with some useful tools for sorting out the good from the bad.
You have some despair in your post about ever knowing anything. There is huge amount of lazy thinking online, where someone will wave their hands and say, well, scholars disagree, you can believe what you like....This is not true: scholars agree about a lot of stuff. We agree there was a Holocaust, that the American Civil War was caused by the South wanting to have slaves, for example. There are mysteries in some matters, and in fields like medieval history historians are often real detectives, thinking very hard about every little clue. There are always different questions being asked, from different perspectives. But this does not equate to, think what you want. And that's a very important bias; the bias of the audience.
Like your teacher inferred, there are stories people like to hear about themselves. Think about computer games, for a moment: they reward you for being clever, intrepid, active, determined and patient. We're each in charge of our own narratives, would like to be the heroes of them, and would like to think those virtues are going to bring us success, and when most people read histories they like the ones that mostly recount how virtuous heroes succeeded. Good v. Bad conflicts are fun, so they also like to read about villains if the villains aren't themselves, especially if the villains are punished ( and , of course, having their villainy revealed in the book makes all the readers part of their punishment) . And, just as people don't like computer games that are purely based on chance- where virtue won't help you- you'll often find a bias for villains and against chance in popular histories, as well ( thus Bill O'Reilly can sell a book that creates a conspiracy around the death of Gen. George Patton, when actually all the evidence shows Patton was just unlucky). So, when you are assessing a history book, a bias to be aware of is how agreeable it's trying to make itself to an audience, playing to their own biases, telling them- and you- what they'd like to hear.