Dealing with Subs

The other day I had an issue with a subcontractor that was EXTREMELY frustrating.  We needed material delivered to the jobsite a certain day and they were not willing to do it.  So, I found another subcontractor who was willing to do it.  It got me thinking... How do I limit myself and my opportunities  by thinking I can't do something?

If someone else can do it, why can't I and if I really can't is there a way to eliminate that roadblock?

What about you?  Do you see this in your life or at work?  Have you removed any roadblocks lately?  Have you exceeded expectations?