A motto that has kept me away from major crashes and injuries:
It's OK to say another day!
I've ridden around 'A-lines' many, MANY times and the funny thing is, after another year or so of progression, you'll go back, take another look and say - yeah, I can do that now.
I love guys in DH Races that feel they have to hit an A-line all the time, then crash while trying to gain a second or so. I always assess the time advantage vs. risk... Save yourself 1 second on a huge step down gap - I'm out. Save yourself 30 seconds on a Gap that you're pretty confident in clearing - then try and hit it. But that's racing.
Riding with your buddies: I'd rather finish the day tired, exhilarated with a big smile on my face and enjoy a beer or two - so yeah, hit the B-lines and have fun! That's what it's all about!