An example of this, though plagued by other problems, is Netflix's The Witcher (2019). Slated to be the new Game of Thrones (2011) - a show that we'll come onto shortly - The Witcher follows the exploits of Geralt of Rivia, ostensibly a harsh, brutal, and violent hunter who breaks hearts and lacks friends. Sort of. Both the novel and video game versions of Geralt actually portray a much softer and more balanced man. And while he still is a fundamentally driven, clever killer, he does love and cherish the people around him.
This, to me, marks one of the most pervasive problems with book-to-screen adaptations - glamorisation. While making a man more of an unapologetic arsehole doesn't necessarily seem to be a glamorous choice, what I truly mean is that it's a creative decision that errs on the side of what Hollywood considers 'mainstream appeal' - shock, gore, and brooding anti-hero based wish fulfilment. Unlike television, which can be propped up by set design, casting choices, and fabulous costumes, novels rely exclusively on their prose and their stories. The difference in form often creates a schism between what the author has created and what a director wants to create, as well as the audience that they're aiming their project at.
This then brings us on to Game of Thrones. Half one of the best shows ever made, half one of the worst. Why? Because of spoilers, they ended their show with a beloved, well-constructed character committing mass murder due to a nondescript coupling of madness and angst that seemed to surreptitiously come into being over the later seasons. Leading to, of course, shock, gore, and brooding anti-hero based wish fulfilment.
Ultimately, the most important part of adaptation is the conveying the book's themes, characters and emotional cores, not just repeating their plots with hot actors and well designed props. Stories are about how they make us feel, and the best adaptations both understand this, and combine it with all the excitements of a visual medium to devastating effect.