Read the following passage and answer the questions that follow:
Some sort of parallel may be found in the way logical connectives are usually unnecessary and often misleading, because too simple. Omitting an adjective one would need ‘therefore’ stressing the adjective ‘although’; both logical connections are implied if the sentences are just put after another. In the same way, people are accustomed to judge automatically the forces that hold together a variety of ideas; they feel they know about the forces, if they have analysed the ideas; many forces, indeed, are covertly included within ideas; and so of the two elements, each of which defines the other, it is much easier to find words for the ideas than for the forces. Most of the ambiguities I have considered here seem to me beautiful; I consider, then, that I have shown by example, in showing the nature of the ambiguity, the nature of the forces which are adequate to hold it together. It would seem very artificial to do it the other way round, and very tedious to do it both ways at once. I wish only, then, to say here that such vaguely imagined ‘forces’ are essential to the totality of a poem and they cannot be discussed in terms of ambiguity, because they are complementary to it. But by discussing ‘ambiguity’, a great deal may be made clear about them. In particular, if there is contradiction, the greater the tension; in some way other than by the contradiction, the tension must be conveyed, and must be sustained.

Why does the author say that “the tension must be conveyed and must be sustained”?