I'm tending to think now that tears and labour in general are just luck. Hear such a wide variety of stories - small babies, big ongoing vagina issues, huge babies, not even a graze. Super fit people having major issues, really unfit people have major issues, super fit people claiming that their fitness led to an easy labour, really unfit people claiming that they'd rested up a lot and dealt with labour easily.
Pah. It's luck. Maybe an element of mind-set afterwards in terms of how you cope with the aftermath and how you think it went for you.
I'm going in to it assuming it'll hurt like a bitch for up to 3 days, it might be scary, it might be traumatic, but on the other hand it might be fine... then it'll be over and human bodies are pretty resilient in coping with stuff.