Think of it like "instinct" vs "thoughtful action"

The very first thing you decide is often an unconscious reaction. Someone jumps at you to scare you and you throw your arms up for example, then you settle down and realize it was just your friend. That's the unconscious making a decision and then your conscious mind taking over. To make conscious decisions you have to evaluate, to make unconscious decisions you just have to react to the immediate stimuli and requires no thinking or evaluation so it comes first and must be corrected.

Continuing the example, if your conscious mind never took back over you would either run or fight your friend but you don't because your conscious mind takes back over as soon as it has made all the evaluations.

Ordering a pizza then regretting it as soon as you think for 5 seconds, mindlessly eating a bag of Oreos, all of these are unconscious actions people take every day (or at least I did and still do to a lesser extent). We can train our unconscious to an extent though, the reason it orders the pizza or keeps eating the Oreos is because that's what we have previously trained it to do. The reason monks can meditate through any sort of scare/pain is they have trained it to not react (though that's an extreme example of course)