When you are in Act 2, there is a level called Introspection
During the very last chapter of this, your shadow will be stuck in a crane
Move the crane with your 3D player until you reach the bird
Jump & catch the bird, then the voice will say to 'Breathe'
During this, just wait with your shadow character for around 15 seconds (which is enough for your 3D character to sit down)
Tab to switch over to the 3D Character and the achievement will unlock