Well, assuming you weren't working during those four years, you actually had negative income, rather than no income.
Though of course if you have dependents it's different. Could be either harder, if you are the main money earner, or easier, if your wife makes enough that you can stop getting salary without sacrificing much.
You got a low-cost education not available everywhere in the world at this time
I got an AA degree from Cabrillo College in 2003 for $2000 and then spent only 18 months at UC Berkeley and graduated from there with a BA degree in late 2004. Sure the cost has gone up since then but still..
With wife, 3 kids, house etc, taking no salary for year is frankly pretty impossible.
Not sure why I am getting downvoted here? I am voicing my perspective.