A couple of guys in my PPL-class failed one or two exams (including nav) the first sitting. They later went on to the ATPL-theory course fulltime and passed all exams there in the first sitting.
As for myself I had a 43% on the first PPL principles of flight due to mixing up terms. Now when thats passed and behind me, it does not seem like a big deal and I'm not gonna let that stop me from taking the fATPL in a future.
Not much but I hoped it helped a little bit...