As I've worked with people at all levels of organizations and in a wide variety of settings, I've observed five common causes of failure in personal relationships, whether in business or at home.  They are:
        Preoccupation with self.
        Hasty assumptions.
        Negative attitudes.
        An all-consuming desire to be liked.
        A disregard for courtesy.

1.  PREOCCUPATION WITH SELF

Nobody likes to deal with the person who is afflicted with the "Big I."  Self-centered people monopolize the conversation, and always turn the subject back to their opinions, their abilities, their accomplishments and their agenda.  They are so concerned about the interests of the "Big I" that they have no time to consider the interests of others.

The word "success" does not contain an "I."  The first vowel is the "U," and until we learn to think "you" instead of "I," our batting average in business and in human relations will be close to nothing.  The best rule for human interaction is still the one pronounced nearly 2,000 years ago from a hillside in Galilee:  "As ye would that men should do to you, do ye also to them likewise."  The surest route to success today is to find out what others want, and look for ways to provide it.  This applies whether you're trying to maintain a healthy and harmonious home atmosphere, sell goods and services in the global market, or align a work force behind an ambitious vision.  Being other-person oriented is a learnable trait.  It often comes naturally with maturity.

2.  HASTY ASSUMPTIONS

People who jump to conclusions rarely land in the middle of success.  We often prejudge people and circumstances by surface appearances without investigating what lies underneath.

A middle-aged man in shabby work clothes walked into the showroom of a Chrysler dealership in Virginia. The salespeople studiously ignored him.

Finally, the owner of the dealership walked over and asked if he could help.

     "How much is that car?" asked the man, pointing to the most expensive model Chrysler offered.
     The dealer told him.
     "I'll take one," said the customer.
     "Very good," said the dealer.  "And how would you like to finance it?"
     "I'll write you a check," said the man.  
     And so he did.  And as he took delivery of his new car, he turned to the dealer once more.
     "By the way," he said.  "Do you sell dump trucks?"
     The dealer proceeded to sell four Dodge dump trucks to this man, who was the owner of a local construction business.

Looks can be deceiving.  Success doesn't always wear Brooks Brothers suits and Gucci ties.  It can also wear jeans and flannel shirts, coveralls and work gloves, or skirts and blouses.
 
3. NEGATIVE ATTITUDES

You may remember the little guy with the unpronounceable name in the comic strip "Li'l Abner," who went around under a perpetual rain cloud.  Wherever he went, things went wrong.

Some people are expert rainmakers.  They bring on their bad luck through negative attitudes.  They know things are going to go wrong, and this faith becomes a self-fulfilling prophecy. 

     "Cheer up," I once told my friend Bob, who seemed always to be on the losing side of life.  "Things could be worse."
     "I know," he said.  "I once cheered up, and sure enough, things got worse."
     "Listen," I said.  "If you just have faith that something good will happen, something good will happen.  I want you to believe -- really believe -- that you're going to have a great day tomorrow."
     At the end of the next day, I called Bob to ask how his day went.
     "Lousy," he said.  "Just as I expected."
     I had another friend, named Charlie, who was just the opposite.  If a load of manure fell on Charlie, he'd say, "Boy, think how this is going to help my strawberry plants!"

No matter what the weather was like, and no matter what his circumstances were, if you asked Charlie how his day was going, he'd say, "Today is the best day of my life."

     I once asked him:  "Charlie, how is it that every time I see you you're having the best day of your life?"
     "Well, Nido," he said, "Yesterday is gone forever and tomorrow is not yet mine.  Today is the only day I ever have, so that makes it the best day of my life."

Charlie died a few years ago, but I'm sure that his reward will be an eternity in which each day is the best day of his life. 

People loved Charlie.  People avoid Bob.  They're afraid lightning will strike them or a tree might fall on them while they're around him.  And it just might happen.

4.  THE DESIRE TO BE LIKED 

It's natural to want people to like you.  We draw strength and inspiration from our friends.  The warm glow of friendship is a great morale booster.  But when you try to buy friendship at any price, you cheapen the product.  You end up not respecting yourself, and others don't respect you either.

You win respect by setting high standards and living up to them.

5.  DISREGARD FOR COURTESY

Some people go to the opposite extreme.  They interrupt people at will, and they say what's on their minds without regard for the other person's feelings.  They think the world should run on their schedule, so they show up for appointments when it's convenient, and if they keep others waiting, that's tough.  Concessions are for weaklings and diplomacy is useful only as a manipulative tool.

Such people may be able to bulldoze their way to success for a while.  But when they encounter reverses and they find themselves in need of supporters, they'll find more gloaters than sympathizers.  

Courtesy is the oil that lubricates the machinery of commerce.  It smoothes the path to success in sales, in management and in personal relationships.