If you run your own business and pour your heart and soul into it, it's easy to be a bit taken aback when things don't go quite to plan and we have difficulties with clients or others who work in similar industries to ours.
One of the issues I regularly coach in is assertiveness in running your small business, and understanding that although your business is the be all and end all to you, as it needs to be, it's a small element in the day to day concerns of other people.
Anything else is simply a lack of perspective and priorities that are out of step.
This, however, doesn't help when a client criticises, or leaves, or refuses to pay, or whatever the issue is.
Clearly we need to develop great relationships and rapport, but sometimes, a business relationship ends.
It's good to care; however, when you know you can't do any more, what happens next? If you are a fairly sensitive person, does it make you feel guilty for charging what you're worth, for example? Do you rarely get paid on time because you feel as if you can't enforce your invoices? Thick skins are needed here.

• Don't take things too personally.
  Most of the time, issues are really not about us.
  Acknowledge they've happened, and then let them go.
  It gets easier with practice.
  
• If you are working with friends, it's going to be necessary to draw up some sort of agreement with them beforehand to keep everything pleasant.
  Nobody likes a falling out, and you can takes steps to prevent this.
  
• Rejection happens to everyone! We're not singled out for this kind of attention.
  Knowing that goes a long way to keeping your head straight when you're running your business.
  
• Are you engaging with your clients? Open and honest dialogue is essential to keep you from guessing and assuming.
  
• Are you worried about asking clients to make decisions that affect when their invoices are paid? Think about what it is that could be causing this and take steps to address it; once again, this is where agreements, terms and conditions and securing deposits come into play.
  
• Do you feel guilty about how much you charge? If so, remember that a business makes money.
  That's its primary function.
  
• Are you on the receiving end of any harsh criticism? This is never fun, so look at where it may or may not be justified.
  Remember that you don't have to accept criticism for the sake of it and you have every right to defend yourself and your work! A balanced view is important to look at room for improvement and so you know which areas to continue business as usual.
  
• If you work in a creative industry, does the business person persona clash with your creativity? If so, it's necessary to separate business you from creative you.
  
• Know your values.
  This is true for all aspects of life; however, one of the perks of self employment is knowing with whom you want to work.
  If there are clashing values, know when to walk away.
  

There are lots of sources out there to advise you on how to structure terms and conditions, ensure payment arrives and so on.
However, it needs to start right at the source, with the business owner, in learning to shake off any feelings of guilt over providing a great service and daring to ask to be correctly rewarded and regarded for it.
Respond to situations appropriately and your business life will be easier to negotiate.
Some of the most successful people I work with have the "water off a duck's back" mentality.
It doesn't mean they are arrogant or don't care.
They simply know how to keep perspective and stand their ground.