A Grand Cosmos's top-grade innate spiritual roots contained Great Dao source, much like holding founding shares, so they were not permitted to be taken out of that Grand Cosmos.
Otherwise, it would amount to permanently losing that portion of its Great Dao source!
And how important was Great Dao source to a Grand Cosmos?
Thus, if you used a Grand Cosmos's top-grade innate spiritual roots as the roots of the five energies for your Golden Immortal foundation, you would never be able to leave that Grand Cosmos unless you could defeat its Heavenly Dao!
Unless you crippled your own foundation and returned the Great Dao source that had merged into your physical foundation!
However, as long as one had yet to comprehend and bear a source Great Dao, reforging either the physical foundation or the primordial spirit foundation was still quite easy. There was a price, but it was not particularly steep.
Once one broke through to Daluo Golden Immortal, however, the physical foundation would have transformed into the flower of essence, and the primordial spirit foundation into the flower of spirit. The three flowers of essence, qi, and spirit gathered above the head, and the true spirit became one.
At that stage, reforging one's foundation was still possible, but the price would be enormous!
The slightest misstep could damage all three flowers of essence, qi, and spirit, impairing one's foundation and leaving the Great Luo Dao fruit teetering on the brink. One might even fall directly from the Daluo Golden Immortal realm to Primordial Unity Golden Immortal.
That would be exceedingly troublesome.
In short, once one bore a source Great Dao, it was best not to reforge one's foundation.
Of course, a foundation could be strengthened at any time.
Reforging a foundation and strengthening it were two entirely different