This is one of my favourite phones of me flying, and it illustrates this point:
I'm being mentored to pick my way into the fog, to continue, because in those mountains, going back is less desirable. The helicopter does not have gyro instruments, so flight out of sight of ground is not safely possible at all.
What was against me: In the mountains, unfamiliar territory, few ways out, nowhere practical to land close by. The helicopter cannot be flown without reference to the ground. Flight over the top would be very unwise.
What I had going for me was an awesome mentor (without whom, I would never have attempted this), I can fly as slowly and low as I need to, and I can turn around. I had the GPS track to follow backtrack.
Indeed, as my mentor predicted, the fog was very local, and picking through it slowly was no problem - he had local knowledge, and that made all the difference! Despite looking very intimidating, I never lost sight of the trees, never slowed to less than 50 knots, and never flew lower than 300 feet above the trees.