Unfortunately, because firms don’t provide feedback, students often think they’re being rejected because they’re lacking something in their experience or grades – and I do understand why you’d think that.
But most of the applications I’ve seen fall down because of the application, not the applicant. It’s always because their application isn’t tailored enough or they don’t sell their experiences i.e. specifically talk about what they did and why that was impressive/what was the outcome.
I’d go so far as to say an objectively weak student who knows how to write about their experiences is much more likely to be accepted than an exceptional student who can’t. That’s how essential it is.