Today I learned that you cannot plug a mini-jack microphone to a MacBook and expect it to work. MacBooks don't amplify their line-in input to process the signal, they require a special gizmo you have to pay extra for.
To learn that I had to scratch Mac's case (and notice high mic signal level), then tap my headphones' mic (and notice no mic signal), then consciously process the information.
This observation makes my everyday habit of connecting headphones' mic to the MacBook and adjusting the mic so other people hear me better just look stupid.
The only upside is that I can still see other guys doing the same ;-)
I wonder how many things there are that I take for granted that actually are false.
The only problem is that to learn that I would need to challenge the obvious - not an easy task.