Your hypothesis dictates your outcome. If you believe that you suck at math, you won't even try to get better at math. As a result, you will suck at math. If you believe that live code challenges are impossible to pass, then you won't put in the work. And as a result, you will fail. Which in turn, of course, will reinforce your belief that you simply suck at code challenges. If you believe in exchange that passing code challenges is simply a matter of preparing well, having a process and practicing enough, then it's more probable that you will put in the necessary work, pass the code challenge and get the job.
Your biggest enemy as a developer many times are your own beliefs. Change your beliefs, change your hypothesis, and you will change your outcome.