Computer problems.
I don't know about other people who build computers, but in all my years working with them, I have always ALWAYS had some kind of issue when putting together a new system from scratch. You really can never tell if something is going to work the way you hope and plan. My latest computer build, I didn't realize the microsoft is stuck in the past, requiring the use of an internal floppy disk to install a 3rd party scsi driver from floppy. I thought I could get away with using current technology (external USB floppy drive), but NOOOOOoooooo. I ordered a UPS to save my computer and my hair from the constant power issues we have on post here in Egypt, but that didn't work because it thinks that 50hz equals a power failure. So I had to buy a second one. The power supply in my box, which is a PC Power and Cooling supply, has a weird issue (not sure if it is my motherboard, an Abit AX8 or the PS) has a weird issue. If I turn off power to the machine, it wont be able to start up unless I leave mains off for an extended period of time.
Then comes the operating system. Whether you choose linux or Windows. In windows, you always need to go through a bunch of bologna to download updated drivers and software, let alone the windows updates. In linux, it's slightly less tedious if you're using a latest build. All you really need to do for major customization is recompile a kernel for your box.
I put together a system once from brand new parts, and had to replace the motherboard right away due to it being faulty.
One guy gave me a laptop to fix that was dead. Turns out it had a family of tiny (and also dead) roaches living inside.
My point is, and has been made by another, is that you can never expect things to go perfectly when you fire it up for the first time. A lot of effort has been put into making this stuff work, and by God it will be done soon!