Work and Human Nature

Why is it almost impossible to separate your work from your regular life? What allows a father to be absorbed in his work enough to cloud his judgment to ignore his children who he works so hard to provide for? His children may never know what he sacrificed for their benefit or the love he had for them. What allows others to completely separate their work from their personal life so that they don't even think of work except at work? Never to worry outside the prescribed working hours. What allows an individual to be absorbed into his work that nothing matters but his job? Never to know a life besides work. How do people find the balance between the two? To be able to talk about work and enjoy it, but not to have it absorb you.