Old (professional) Adam

Solution 1:

Congratulations on spotting the right reference in Wiktionary. The Old Adam is, Merriam-Webster tells us, "unregenerate human nature", quoting the Book of Common Prayer: "grant that the old Adam in this child may be so buried". It's the ineluctable tendency of fallen humanity to revert to its original sin.

And in Smiley's world, from novel to novel to novel, the cardinal sin, the trap which the professional spy must be most wary of falling into, is pridefully believing that he and his agency are knowledgeable and competent.

So Smiley must school himself not only to confess his past failure but also to suppress his hybristic assumption that he now understands what happened and is therefore capable of rectifying the situation.

But this is straying off-charter, into literary criticism.