פירוש על בבא מציעא 3:6

Gemara - I saw it: Before you picked it up.

He acquired [it] through sight. The Gemara is suggesting that if the Mishna had only written - אני מצאתיה - I found it - one might think that the litigant is claiming that I saw it first and that by seeing it, he acquires the garment. The second phrase of the Mishna - כולה שלי - it is all mine - indicates that seeing is insufficient for acquiring a lost object. One must actually lift up the garment to acquire it.
Tosfos will quote two Mishnayos where it is evident that one cannot acquire a lost object by seeing it. If so, why was it necessary for our Mishna to repeat the same ruling?
The Mishna on 9b: Even though the Mishna teaches (below 9b): [Ruvain] who saw a lost object and said to [Shimon] “give it to me”. The Mishna rules that Shimon who was asked to pick it up may acquire it for himself. We see that [Ruvain] did not acquire it by seeing it, since Ruvain who asked Shimon to pick it up, obviously was the first to see it and even so Shimon may lift it up for himself. It is evident that Ruvain did not acquire it by seeing it.
The Mishna on 10a: So too, we learned in another Mishna: [Ruvain] saw a lost object and fell on it, but did not lift it up and Shimon comes and lifts it up, the Mishna teaches us that [Ruvain] did not acquire it since he did not make a proper act of acquisition. But Ruvain did see it first? Once again we see that seeing the lost object is not a way of acquiring it. Why does our Mishna need to stress this lesson?
[The Gemara] could have deflected the proof from those Mishnayos, that seeing is not an act of acquisition, by saying, since [Ruvain] said to Shimon in the Mishna on 9b “give it to me”, or in the Mishna on 10a he fell on it, he is showing his mindset, that he is not satisfied to acquire it by any method of acquisition until it actually reaches his hand. It is only then that those Mishnayos rule that seeing the lost object is not a valid method of acquiring it. However, when one did not in any way indicate that he does not want to acquire the lost object by seeing it, it may very well be that seeing is a proper way of acquiring it. Our Mishna must therefore teach us that even when there is no indication that he is dissatisfied to acquire it by seeing, he cannot acquire it.

He acquired it through sight: From that which it taught, "They divide it."

"He teaches, "All of it is mine": With complete control, since I picked it up first, and you grabbed it from my hands after I acquired it.