“I was to test my thinking by the new God-consciousness within. Common sense would thus become uncommon sense.” (Page 13, Big Book)
This is a tricky line. Obviously common sense—the faculty of the intelligent and fair assessment of circumstances—is not lost by working the programme. It does not therefore cease to exist by substitution.
What I think this is referring to:
There are times one prays and the solution appears the opposite of what most people might think or do. ‘Uncommon’ is the opposite of ‘common’. God’s solution is the opposite of the ordinary human solution.
This opposite is sometimes a positive action (going and settling matters or being cordial or even friendly with people one dislikes) and sometimes a negative action (letting go entirely rather than hammering at the problem with obsessive thinking and self-will).