Captain Obvious points out the sheer lack of common sense you occasionally see in others, like:

I am leaving for a camping trip shortly and I am brought to recall the frequency with which I see people struggling to put up a tent straight out of the box. You'd think it would have occurred to them to have done a dry run before heading out. Similarly I've had to lend people cannisters of fuel because it didn't occur to them their camp stove would need one. You would have thought that would have been obvious. And I've had to teach people to build a fire because they didn't realise you can't start a log on fire with a lighter. Shouldn't finding some kindling be clearly obvious?

Okay, so I had a bit of a brain freeze myself recently. I scratched my head over and over because my DVD player wasn't working. My son came over, pulled out the HDMI cable from the android box and plugged in the DVD. Smack the forehead. d'uh.