1234 Chords

1234 is played in drop D tuning, this mean that you detune the 6th string from an E, to a D.
All Chordacus images are because of this not the same as in the video.

Your aim for this lesson is to still visualize the normal chord shape, replacing the root only.
Simply imagine the entire shape, don't just focus on the root note.

The verse use a simple I - I/VII - VI - IV progression which gives the track a descending feel.
The chorus use a V - IV - V - IV progression to build ourselves up again for the verse. 

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Together these two progression create a loop that drive the track forward.

The single line variation at 1:04 doesn't sound strange since the chord progression by now is so ingrained in us, only referring to its descending pattern is enough.
This is a great trick when in need of creating a breakdown section out of nothing.

When you properly go for it in the last chorus the effect is more dramatic since the difference in dynamics is more extreme.

A, A shape A, E shape Bm, Am shape D, A shape G, E shape G, G shape D, C shape