I have a different philosophy. I assume I will NOT get the job so therefore I'm not very stressed.
Let's me feel very free during interviews and I'll say whatever I think. I'll make jokes and I'll even call out the interviewer if they ask something crazy "okay I'll answer but did you just Google that question?".
I once had an interview where the guy said "we only hire the best and brightest here, and you might be a good fit, what do you think about that?"
I said "I don't think this a good fit for me". The guy was bewildered. I said "yeah I want to work with the dumbest and laziest people. I think I'm pretty good but if I'm competing against the best it's going to be harder to stand out. I'd rather work with the worst"
He was really floored and laughed and told me he really respected my view though. Idk, if I had worried about doing a good job I wouldn't have said that.
I'm not sure what my point is but I guess it's just that if you don't worry about getting it you won't be as nervous.