It is key.. I think it's the first thing that should be taught to children and new learners.. I'm always surprised to find that new players have not learned the basics of tuning yet.
... and it's a whole different experience learning to tune on stage. You may tune fine in a quiet room.. try it where you can't hear or see your guitar. I always suggest if you're looking to play in public, get you some good jokes to say while you tune; especially for those particular bad tuning nights.