[4] Since "the man of inferior De" takes action on purpose, he is apt to encounter the probabilities of either success or failure in fulfilling his objectives.
[5] The expression "without purpose" means "without the purpose of exhibiting humanity or of extracting from others any responses or favors in return."
[6] The expression "on purpose" means "action(s) deliberately taken to exhibit righteousness and expect in return something favorable."
[7] The statement implies how the advocators of propriety act against the principle of take-no-action or the way of naturalness by imposing their value systems upon others. Lao Zi's critique of this "action" is discernably sarcastic.
[8] This version is based on the rearranged line gu shi dao er shi de according to the philological studies done by Gu Di and Zhou Ying (see Lao Zi Tong, pp. 278-279). This is based on the fact that the Dao and De are inseparable, like the two sides of the same coin. The interrelation between the Dao and De as such threads through Lao Zi's philosophical system. Yet, in some editions of the Dao De Jing the line goes: gu shi dao er hou de ("Only when the Dao is lost does De arise"), which seems to make a distinction between the Dao and De in the sense of time sequence on the one hand, and treats De as a value paradigm independent of the Dao on the other. This seems to be logically problematic with regard to the entirety of Lao Zi's doctrine.
[9] The phrase dao zhi hua can be translated literally as "the flower of the Dao" and figuratively as "the ornament of the Dao," suggesting the appealing surface or superficial appearance of the Duo. It is still far away from "the fruit," i.e. the substantial truth of the Dao.
[10] "The great man" stands for the Daoist sage. "The thick" is explained by Heshang Gong as meaning "simplicity, honesty and sincerity." I think "the thick" in this context refers to what is adequate, like the "superior De," while "the thin" refers to what is inadequate, like "propriety" (li, which also means "rite," "ceremony," "ritual," or "code" as well as "norms" of conduct).
[11] As mentioned above, "the fruit" is figuratively used for the substantial truth of the Dao, whereas "the flower" is used for appealing appearance of the Dao as is reflected in "superior humanity" (shang ren), "superior righteousness" (shang yi), etc.
[12] Lao Zi encourages people to approach the "superior De" as the truth of the Dao rather than the "inferior De" as the appearance of the Dao involving humanity (ren ), righteousness (yi) and propriety (li) all together.

Commentary:
In this chapter Lao Zi presents his hierarchy of values comprising the "superior De" and the "inferior De" as its two broad categories. The former is highly recommended as the manifestation of the Dao. It is characterized by its adhesion to the principle of "take-no-action" or the way of spontaneity. Likewise "the man of superior De" is, according to Lao Zi, an ideal personality to be imitated by all walks of life, for he is the one who has attained the genuine Dao.
In view of the latter, its elements go downward from "superior humanity," through "superior righteousness" to "superior propriety" which were officially appreciated by the ruling class then and persistently advocated by the Ru Jia (which was later developed into "the school of Confucianism") ever since. If considered from Lao Zi's perspective, they all tend to deviate from the way of naturalness and the principle of take-no-action no matter whether or not they aim at self-exhibition and favorable returns. Hence they may show inadequacy in doing this, and weakness in doing that; or worse still, they may be reduced to mere pretentious protocols which restricts their behavior and puts them in mental straitjackets. History has shown that it would be employed, more often than not, by self-seeking people.
Lao Zi expresses his preference for the "superior De" for being symbolic of simplicity and sincerity in one sense, and corresponding to his philosophy of taking no imposing action in the other sense. At the same time, he tenders his critique of the "inferior De" since it works the other way round. This also reflects his nostalgia for Daoist innocence and plainness, and his anxiety derived from his observation that social instability results from damage to and desertion of the Dao, and meanwhile from the propagation and application of other low-brow values such as "humanity" (ren), "righteousness" (yi), and "propriety" (li), etc.
Incidentally, the "fruit" of the Dao is plain, true and associated with the "superior De," whilst the "flower" of the Dao is dazzling, false and connected with the "inferior De" as has been described above.

(1)(2)(3)