“Combinatory play,” said Einstein, “seems to be the essential feature in productive thought.”
Ruminating on the necessity of both reading and writing, so as not to confine ourselves to either, Seneca in one of his Epistles, advised that we engage in Combinatorial Creativity — that is, gather ideas, sift them, and combine them into a new creation.
We should follow, men say, the example of the bees, who flit about and cull the flowers that are suitable for producing honey, and then arrange and assort in their cells all that they have brought in; these bees, as our Vergil says,
Pack close the flowing honey,
And swell their cells with nectar sweet.
It is not certain whether the juice which they obtain from the flowers forms at once into honey, or whether they change that which they have gathered into this delicious object by blending something therewith and by a certain property of their breath. For some authorities believe that bees do not possess the art of making honey, but only of gathering it … Certain others maintain that the materials which the bees have culled from the most delicate of blooming and flowering plants is transformed into this peculiar substance by a process of preserving and careful storing away, aided by what might be called fermentation,— whereby separate elements are united into one substance.
But I must not be led astray into another subject than that which we are discussing. We also, I say, ought to copy these bees, and sift whatever we have gathered from a varied course of reading, for such things are better preserved if they are kept separate; then, by applying the supervising care with which our nature has endowed us,— in other words, our natural gifts,— we should so blend those several flavors into one delicious compound that, even though it betrays its origin, yet it nevertheless is clearly a different thing from that whence it came.
Montaigne, perhaps echoing Seneca, reasoned that we must take knowledge and make it our own, Seneca comments:
We must digest it; otherwise it will merely enter the memory and not the reasoning power. Let us loyally welcome such foods and make them our own, so that something that is one may be formed out of many elements, just as one number is formed of several elements whenever, by our reckoning, lesser sums, each different from the others, are brought together. This is what our mind should do: it should hide away all the materials by which it has been aided, and bring to light only what it has made of them. Even if there shall appear in you a likeness to him who, by reason of your admiration, has left a deep impress upon you, I would have you resemble him as a child resembles his father, and not as a picture resembles its original; for a picture is a lifeless thing.
The Loeb Classic Library collection of Seneca's Epistles in three volumes (1-65, 66-92, and 92-124), should be read by all in its entirety. Of course, if you don't have time to read them all, you can read a heavily curated version of them.