There's a difference between 'turning back' and 'looking back' ...yet, both are conditional. What I mean to say by that is ...well, let me just say, there are times when both are a positive thing to do, and there are times it is not the best thing to do.

We have two kids in driver's education right now.  They must utilize their rear view mirror, and look back. That is definitely a good thing.

You are driving down an old dirt road, and encounter a roadblock.  A sign tells you to turn back ...the road ahead is washed out.  There had been a heavy rain recently.  It would be advisable to heed the warning, and turn back ...and it's also a good thing for drivers of all ages to not disregard traffic signs.

When is it not good to turn back?  

You are going to visit your brother who is in the hospital.  You start out, and begin to have those worrisome feelings again.  You haven't been on good terms with your brother, and have second thoughts about visiting him.  Well, it is my belief that you should not turn back.  Your brother is ill, and this is probably a good time to put the past behind you and try to make good with your brother.

When is it not a good time to look back?

I guess the tough lesson is what Lot's wife experienced.