The two reasons overlap a bit. My computer is partially built by me, but it isn't completely built by me. I upgraded a few things. One of the things I upgraded was the graphics card, which generates the most heat. The graphics card I got generates an amount of heat that my computer isn't built to handle, so whenever I play certain games, it overheats and shuts down. It's incredibly annoying.
I got a fan to try to cool it enough to play the games without overheating, but there was no where to plug it in on my motherboard. (Thanks store bought computers) I tried to wire it to an outlet plug and a switch and just plug it in near my computer and duct tape it to the case, but Franklin short circuited it. Seems like him, doesn't it?
I got an EL (Electroluminescent I think) wire to put in my computer. Its basically a long wire that lights up when the computer is on. When I went to install it in my computer, I found that there is no where for me to plug that in either.
I would have built my computer entirely myself, but I didn't for a few reasons.
1) Costs like twice as much
2) Unreliable (Right, Franklin?)
3) Takes too long
4) Easy to mess up
I probably should have explained more things and terms and stuff than I did, so if you have any questions just ask in the comments.