Let me see if I can paraphrase Peirce’s triad. 

The elements of the triad are distinguishable, but inseparable. They cannot be grasped in isolation, but articulated against the whole to which they belong. Peirce said they are to be prescinded, not isolated. 

Firstness is the immediate qualities of experience, including the entities experienced. It is monadic. It is experience experienced. 

Secondness is the brute reality of experience, most conspicuous in surprise. It is dyadic, composed of effort (of doing, or understanding) and resistance (to doing or to being understood). Secondness is encountered existence. 

Thirdness is — not sure about this — the concept — which is understood in terms of its full pragmatic consequence (a bundle of experienced beliefs each of which manifests with experience as firstness) of a meaningful entity. It posits, predicts, expects, establishes norms against which secondness will accord or discord. Thirdness is understanding that seeks to intelligibly integrate existence (universality) with encountered existence (pluralities).

Firstness is experience.

Secondness is encounter.

Thirdness is meaning.

Without firstness, secondness and thirdness have no material by which encounter or understanding can occur. No monads = nil.

Without secondness, firstness lacks resistant entities to stand out against the experiential flux, and without such entities thirdness is deprived of anything to understand. (No “intentional object” can emerge for thought.)

Without thirdness, firstness and secondness are indistinguishable. Thirdness supplies meaning; meaning animates effort, which invites resistance, and constitutes secondness. The distinction between what is experienced and what is encountered cannot be made.

What I am missing, and what makes me question the completeness of my understanding is this: isn’t firstness possible without secondness and thirdness? Second and thirdness seem interdependent in a way firstness does not. It might be a psychological fact that firstness is always accompanied by the other two elements, but it strikes me as philosophically unnecessary unless we impose a tautological definition that says that experience is only such in the context of the full triad.

So the thirdness that is my understanding of Peirce’s triad is encountering some resistance (thwarting some of what I would expect him to say) that leads me to wonder if Peirce’s idea (its stubbornly real secondness) is other than what I have made of it (thirdness), and in the context of this secondness and its disruption of my own expectations (firstness produced by thirdness?) it is leading me to experience the firstness of his words and his philosophy as a whole (also firstness) with some anxiety.