This article was a big surprise to me. The gist is that using the executive function of your brain (switching from deliberation to implementation - making and acting on decisions) has a strong negative impact on all sorts of mental activities.
For example, deciding whether to have cake or cornflakes for breakfast could be enough to make you perform poorly at an interview later on.
A further implication of this (to me) is that people who coast through much of the day like zombies (especially in the morning), not making many decisions, are much better able to perform when they need to, because they haven't depleted those resources yet.
The moral of the story: if you want to improve your overall mental performance, get into the habit of saying "who gives a shit?" about irrelevant decisions like where to put the furniture or whether the curtains need to be washed again this week. Don't deliberate over mundane issues. Don't waste your energy. Just pick the first reasonable option. I'd like to know if strategies like this can minimise this effect, or if we really have to go around like cattle - I know I do, most of the time... Is that what girlfriends are for? To decide where the couch and TV should be and what washing powder to use, so that I can reserve my brain power selfishly for 'clever' use later (which rarely happens)? Seems a little unfair, really...
I have more questions. How do we recover from the effects? How long does it take? Can we speed it up? What about meditation, or induced alpha/theta/delta brainwaves (i.e. by listening to binaural beats, say)? Why does it happen?
Enough rambling (I guess...), I'm off to dodge some decisions! Probably.