Kinyan 20 Mi'ut Derech Eretz - Rav Avigdor Miller, Make Time To Live
A friend of mine once shared with me the following insight. After about a month in law school he figured out the following revelation. If he puts in long hours studying and worked very hard in law school he would be rewarded by receiving a high paying job that would require him to work even harder and put in even more hours. If he succeeded in that task over many years, he would be rewarded by being made partner receiving even more money and working even harder. At some point he'd be making so much money that they'd throw him out and he'd spend the rest of his life working even harder to prove that he is better than they are.
The Maharal MiPrague explains Mi'ut Derech Eretz to mean limiting the your working hours. There are only so many hours in the day and if you spend all of them working with little time for learning, don't be surprised if you don't become a big talmid chochom, no matter how smart you are or how many degrees you have.
Isn't this the same as Mi'ut S'chora, limiting your business activity? Derech Eretz is actual work. While less stressful if you work for others, nevertheless the hours are long since you are being paid for services, and the boss wants you to work hard. S'chorah, is the businessman that need not put in long hours. Nevertheless his head is consumed with his businesses. If he is involved in too many things he may have the time to learn, but he won't have the head for it.
Rav Avigdor Miller once said, "Learning mussar teaches you how to live, but learning Bava Kama is living". We need to earn a "living" somehow either as employee or an entrepreneur. But either way, if its a full time thing, what is the point if you will have no time to actually "live".