I am quite familiar with Paul's admonishing that, if we could get to heaven by being nice people and doing good works, it would make our heads swell as if we had something to boast about (Eph 2.9).
I can easily relate.
But I had never related to the fact that Paul is writing the same thing to the Romans (4.2):
For if Abraham was justified by works, he has something to boast about, but not before God.
And the way Paul says it to the Romans warns me that--should I feel like boasting--I should just make sure that God does not hear it!