tatraivaḿ sati kartāram
ātmānaḿ kevalaḿ tu yaḥ
paśyaty akṛta-buddhitvān
na sa paśyati durmatiḥ

Translation of Bhagavad Gita 18.16

Therefore one who thinks himself the only doer, not considering the five factors, is certainly not very intelligent and cannot see things as they are.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

A foolish person cannot understand that the Supersoul is sitting as a friend within and conducting his actions. Although the material causes are the place, the worker, the endeavor and the senses, the final cause is the Supreme, the Personality of Godhead. Therefore, one should see not only the four material causes but the supreme efficient cause as well. One who does not see the Supreme thinks himself to be the doer.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

Then what happens? Though these five are causes of action (tatra evam), one who sees only the self, the jiva, as the doer, without association of anything else, does not see, being a fool (durmatih), because of impure intelligence (akrta buddhitvat). One may say that such a foolish person is blind.

Commentary by Sri Ramanuja of Sri Sampradaya:

18.16 In fact, the agency of the individual self is subject to the consent of Supreme Self; such being the case, if the ‘individual self regards Itself as the agent,’ It is of wicked or perverse mind. For, It does not perceive the agent as It really is, since It possesses an ‘uncultivated understanding,’ namely, an understanding which does not reveal the real state of affairs.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

So what then is to be concluded? Lord Krishna states that the five previously mentioned causes are responsible for all actions and one who due to ignorance from lack of knowledge from the spiritual master regarding the Vedic scriptures and in their folly regard themselves as the perpetrator of action instead of attributing all actions to the supreme absolute reality which is completely spiritual and free from all limiting adjuncts and not subject to material considerations are fools and deluded.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Here the word kevalam means solely. Those who in ignorance are unaware that all actions are enacted collectively by the five previously mentioned causes and erroneously thinks that the individual is the sole performer of any action are merely misguided fools of miniscule intelligence.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

Now Lord Krishna explains that not withstanding the positive merits or negative demerits of actions performed by the mind, speech and body. One who is untrained, unrestrained and undeveloped is due to lack of instructions from the Vaisnava spiritual master who teaches the knowledge and import of the Vedic scriptures. Such ignorant and misguided fools who ignore the Vaisnava spiritual master who is always in the line of authorised disciplic succession from one of the four authorised sampradayas or channels of spiritual knowledge as confirmed in the Padma Purana and Garga Samhita; believe that they alone are the sole cause of their actions and not the five previously mentioned factors. Such miscreants are so deluded by this distorted mentality that they are oblivious to the fact that their very existence and everything else existing in creation is irrevocably dependent upon the Supreme Lord.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

18.16 Tatra is used for connecting with the topic under discussion. Tatra evam sati, this being the case, when actions are thus accomplished by the five causes mentioned above;-this portion has to be connected with ‘perverted intellect’ by way of causality [Actions are done by the body etc., but since a person thinks that the Self is the agent, therefore he is said to have a perverted intellect.]-yah, tu, anyone, an unenlightened person, who; pasyati, perceives; kevalam, the absolute, pure; atmanam, Self; as the kartaram, agent-thinking, ‘I myself am the agent of the actions being done by them’, as a consequence of imagining the Self as identified with them; why?-akrta-buddhitvat, owing to the imperfection of his intellect, owing to his intellect not having been refined by the instructions of Vedanta and the teachers, and by reasoning-. Even the person who, believing in the Self as distinct from the body etc., looks upon the distinct [Ast. omits anyam (distinct).-Tr.], absolute Self as the agent, he, too, is surely of imperfect intellect. Hence, owing to his having an imperfect intellect, sah, that man; na, does not; pasyati, perceive (properly) either the truth about the Self or about actions. This is the meaning. Therefore he is a durmatih, man of perverted intellect, in the sense that his intellect is contemptible, perverse, corrupted, and the cause of repeatedly undergoing births and deaths. He does not perceive even while seeing-like the man suffering from Timira seeing many moons, or like one thinking the moon to be moving when (actually) the clouds are moving, or like the one seated on some conveyance (e.g. palanquin), thinking oneself to be moving when others (the bearers) are moving. Who, again, is the man of right intellect who perceives correctly? This is being answered:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

18.13-17 Panca etc. upto na nibadhyate Conclusion : the established end, because here a decision is arrived at. Basis : the material object Destiny : the good and bad result [of actions] previously accumulated. These five viz., the basis etc., constitute the entire assembly of factors and hence they are the causes for each action. But other [commentators give an etymology of] adhisthana ‘basis’ to mean ‘That by which all actions are governed’; and on that ground they believe that it denotes that action which exists in the intellect; which comes ot be due to the Rajas, and is being prone to transform itself into the pentad of (the mental dispositions viz.) the content, the faith, the happiness, the desire to know and the aversion to know; which is referable by the term karma-yoga (that which yokes man into activity); and which is described at times by the term prayatna ‘effort’. Agent : the ascertainer characterised by the intellect. Instrument : [the personal instruments viz.] the mind, the eye etc., and also the external ones like sword etc. Activity : the activity of upper life-breath, nether life-breath etc. The effects of the righteous and unrighteous acts are indicated by the term Destiny. All the dispositions located in the intellect are indicated by these two. Still other commentators, however, take Basis to be the Absolute Lord. Due to his imperfect intellect : because of his having indecisive knowledge. But he, who performs actions with the stability due to disappearance of th I-sense (limited) and [a stability] refined by hundreds of reasoning, as detailed earlier – he does not get the fetter, because he is a man of perfect intellect. This is what is intended [in the passage under study].

Sanskrit Shloka Without Transliteration Marks:

tatraivam sati kartaram
atmanam kevalam tu yah
pasyaty akrta-buddhitvan
na sa pasyati durmatih

Sanskrit to English Word for Word Meanings:

tatra — there; evam — thus; sati — being; kartāram — the worker; ātmānam — himself; kevalam — only; tu — but; yaḥ — anyone who; paśyati — sees; akṛta-buddhitvāt — due to unintelligence; na — never; saḥ — he; paśyati — sees; durmatiḥ — foolish.