Another habit not quite so odious is belittling ourselves. This might seem to be the exact opposite of boasting, but actually it is the same old sin traveling under a nom de plume. It is simply egoism trying to act spiritual. It is impatient Saul hastily offering an unacceptable sacrifice to the Lord.
Self-derogation is bad for the reason that self must be there to derogate. Self, whether swaggering or groveling, can never be anything but hateful to God.
Boasting is an evidence that we are pleased with self; belittling, that we are disappointed in it. Either way we reveal that we have a high opinion of ourselves. The belittler is chagrined that one as obviously superior as he should not have done better, and he punishes himself by making uncomplimentary remarks about himself. That he does not really mean what he says may be proved quite easily. Let someone else say the same things. His eager defense of himself will reveal how he feels and has secretly felt all the time.
– AW Tozer –
From Man – The Dwelling Place of God, ch. 18, “Boasting or Belittling”