This is the most useful thing you can learn while eating curry, drinking beer and watching TV.
Seen House? Know what the differential is?
It's where someone works out what the problem is just be the presence of some information. This is differential diagnosis.
Differential diagnosis is very similar to Occam's razor in that you work from the most probable cause, then through to the least probable. You try to disprove each cause, thus proving you should carry on through the causes.
In particularly confusing cases, or where you have to agree as a team what cause to investigate first, the differential can be an arbiter.
Start by writing down all the symptoms. You'll need to brainstorm these as chances are you see a symptom as a completely normal feature, but you need to have a full list of possibilities. Don't be tricked; symptoms are just the current behaviour of the system.
When you have the symptoms listed, it's time to list the causes. Against each symptom list everything that could cause it, even slightly and even if it's unlikely. You can really go to town here because the next stage eliminates the stupid and ridiculous ideas with the help of Occam.
With the possible causes next to each of the symptoms you simple look first at the cause with the most symptoms present.
There are two routes forward. You can use Occam's razor by looking at which line is most likely or you can look at the cause which has the most symptoms.
The differential takes the most likely cause and runs with it. You then have to prove it true (or not false), and you're away.
