Being a software guy by nature, I'm used to very rapid design and implementation turnaround. You edit the source code, compile it, upload it, try it, find bugs, lather, rinse, repeat.
What's chafing my hide now that I'm doing hardware projects is that the turnaround time to get a PCB fabricated is 2 weeks.
All I can do in that 2 weeks is obsessively go over the design that I've already paid for. Sometimes I wind up finding a whopper of a mistake and have to order a new design. Then I still get to wait a week to receive a package in the mail with my mistakes in it. I open the envelope, smirk, and throw the boards right in the trash. It's disconcerting.
My latest mistake is that I thought a particular part that I want to use was some sort of narrow variant of a SOIC-8 package. Um, no, it's an MSOP-8. It's much smaller. There's no way the leads are going to fit the pads on the board. So the first two versions of the Toast-R-Reflow controller that I've ordered are all garbage.