Not getting the job done is a big issue when you have people working for you.
When they have Too Much Confidence and say they have no problems doing anything you ask, when the Job doesn't get done, you are left frustrated and annoyed.
Another issue is Lack of skills and they don't have the confidence to say that they don't know how to do it. You either wait for them to learn or they hope if they delay, you will find someone else to do it which is annoying.
Have you found out they are Over committed? Finding that they haven't done your work because they are working for someone else makes wonder why you wasted your time.
Not understanding what you want is another big issue. Both of you are waiting on the other to do something, and nothing gets done.
I recommend to always start with one small job at a time. It's worth the time to get it right! http://businesssolutionsanalyst.com