Driving 14 hours in a day is doable and safe for some people.
However driving 14 hours a day can be very tiring and not recommended.
If you do need to drive 14 hours in one day make sure to get plenty of sleep the night before and pull over as often as possible to stretch your legs and get something to eat.
If you start feeling tired then pull over somewhere and stop driving and get some rest.
When I was 18 to 20 years old I could easily drive 14 hours in one day but now that I'm nearing 40 years old I can no longer safely drive 14 hours in a day.
Driving 8 hours in one day is enough for me.
In my opinion though it's not really safe for anyone to drive 14 hours in a day and it's not recommended even though some people can do so.