Watch the Captain have a Eureka moment with chords in keys :) hope it might help you have one too!
View the full lesson at Rut Busters ep.6 What Key Am I In? | JustinGuitar
The chord progression that The Capitan was playing sounded like Mac The Knife to me!
Not sure if anyone’s still monitoring this thread, but I found this Playground’s video from the Rut Busters series while I was going through Grade 3 Module of the Practical Music Theory course, and I’m struggling at the end to understand why is the song Slow Dancing In A Burning Room in the key of E, I played and replied the same section of the video over and over again but can’t quite understand where he got the I, VI, IV progression… I’d be very grateful if someone could be kind enough to walk me through it… 
The chords are C#m A and E with a F#m in the chorus. The chords in the key of E are E F#m G#m A B C#m Ddim. So in order of the chord it would be VI IV I.
Cool. I played four random notes on my bass because they sounded good. D# A# C G#. Played the chords and came up with D# A#m Cm G# which should be a 5-2-3-1 progression in the key of Ab. I played them on guitar then bass. Sounds nice, seems to work, but I don’t think it’s what I’m thinking it is. Or maybe it is. So I’m confused. Or I’m so confused. My brain’s melting. Gotta hang it up for the night.
One thing I did pull out of this which was a light-bulb moment - I now see how to construct a scale using chords. I can play the first six intervals without a problem but the 7th interval diminished is a bear. But? Still cool!
You need to rethink your work there are no #'s in the key of Ab
Laughs. Where would I be without you dear stitch. A-wandering away far afield I dare say. Ah good person, but I did say “So I’m confused,” and “My brain’s melting.” And it was!!!
New day:
“Played the chords and came up with Eb Bbm Cm Ab which should be a 5-2-3-1 progression in the key of Ab.”
Should I stray asunder, do feel free to give me a good, hardy virtual slap. You’re the best 
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Interesting as this lesson has led me down the path of playing scales using chords. I always wanted to know how to do that, and now - “Ta-da!” I can do it.
However, one note of interest is the sound of the diminished 7th - Ugggh. What a strident sound. If your major chords are Old Yeller finding his way home, and minor chords are Dr. Zhivago having a heart attack as Julie Christie rides away, then the 7th dim chord is like opening the door to your Carpathian farm-house and finding the Werewolf eating your pet cat. What a sound! But nonetheless, it’s a fun exercise.
I think that certain types of extended chords sound better on other instruments or within a richer harmonic context. I checked the Wikipedia article on diminished 7th chords and none of the soundbites there sound particularly bad to me. Strange, yes (that was often the point of using this chord) but bad, no.