How competitive are assessment centres?

I’ve been applying to summer internships and so far I’ve got to two assessment centres (one virtual and one in-person) and failed both. One was actuarial at WTW and the other audit at a big 4 firm.

From looking around, people seem to say if you get to an assessment centre you’re ’basically hired’ and that’s it’s harder to fail than succeed at this stage (especially for big 4 assessment centres).

Given I’ve got another two assessment centres coming up soon, I’m wondering if it’s me that is the problem, or if it’s just that summer internship applications are far more competitive than graduate roles, even at the assessment centre stage? (And that while a majority of those who get through to the AC stage for a graduate role might succeed, this may not be the case for summer internships).