Competion in Business- hassagas Gevul

 Why are there many halachas against economic competition when at the same time we have the widespread belief that is expressed in the gemora that a person only gets what G-d has decreed?

Yoma (38b): By your name you will be called, to your place you will be restored and from what belongs to you will you be given. No man can touch what is prepared for his fellow and One kingdom does not interfere with the other even to the extent of one hair's breadth.

Bava Basra (21b)  If a resident of an alley sets up a handmill and another resident of the alley wants to set up one next to him, the first has the right to stop him, because he can say to him, ‘You are interfering with my livelihood.’ May we say that this view is supported by the following: ‘Fishing nets must be kept away from the hiding-place of a fish which has been spotted by another fisherman the full length of the fish's swim.’ And how much is this? Rabbah son of R. Huna says: A parasang?’ — Fishes are different, because they look about for food.

Chavos Ya'ir (Teshuva 42) King David praises one who does not enter his fellow's trade.(Sanhedrin  81a)  David considers this trait a sign of piety precisely because it is technically permitted (as long as one is a local resident). David commends one who refrains from competing with his friend for going beyond the letter of the law.

Divrei Hayyim (CM 56) The custom of prohibiting the purchase of books from any printer who encroached on the rights of another printer "was based on the words of the geonim who preceded us," and was conditional upon a significant rabbinical figure having agreed to the publication by the first printer. He added that this prohibition had acquired the status of a custom, and was therefore valid even if it was contrary to the laws of the Torah.

Igros Moshe (Choshen Mishpat 1:38) A number of congregants of a particular shul formed a ‘breakaway shul,’ whose popularity soon exceeded that of the original shul. Most of the members of the original shul joined the new shul, denying the Rabbi of the original shul the income he had been making from membership fees. The Rabbi in question had bought the shul property some three years prior, and the breakaway shul had caused him serious financial harm.In spite of the congregants’ claim that the liturgy of the original shul confused them, and that it was hard for them to cope with the Rabbi’s angry outbursts, Rav Moshe rules that the congregants were not allowed to break away from the shul. Citing from the Chasam Sofer and the Aviasaf, he explains that the severity of the prohibition of cutting off somebody’s income cannot be offset by the congregant’s claims. It is important to note that a number of congregants did remain in the original shul, and therefore the income of the Rabbi was not entirely ruined. Nonetheless, Rav Moshe writes that “because the congregation has become so small, so that the income is insufficient for his needs… this is certainly a prohibited case of ruining another’s income.”

Nida (52b) Job blasphemed with the mention of tempest and he was answered with a tempest. He blasphemed with the mention of tempest, saying to Him, Sovereign of the world, perhaps a tempest has passed before Thee, and caused Thee to confuse "Job" with "enemy"? He was answered with a tempest: Then the Lord answered Job out of the whirlwind, and said to him, Most foolish man, I have created many hairs in a man's head and for every hair I have created a separate follicle, so that two should not suck from the same follicle, for if two were to suck from the same follicle they would impair the sight of man.

Rabbi Moshe Sternbuch (Teshuvos Ve-Hanhagos 1:800) It is permitted for somebody to open a rival restaurant next to an already existing restaurant . However, if prices are much lower than those of the rival restaurant, so that the existing restaurant will be unable to compete, it would be forbidden to lower prices, and drive the existing restaurant out of business. The prohibition will not apply when only a number of items are sold at the lower price.

Sanhedrin (81a) What is meant by, neither hath defiled his neighbor's wife, indicating that he did not competitively enter his neighbour's profession;

Shelah (Shavuos 183:2).: "It is a great principle to report sayings in the name of those who said them, and not to steal sayings from those who said them, for such theft is worse than stealing money… How great, in my eyes, is the sin of a person who cites an interpretation that has been published in a book, or which he has heard, and fails to mention the name of the original maker or writer of the interpretation" 

Sifrei (Devarim 188) "You shall not move back (into his own land, thus broadening your own, the boundary marker of your neighbor." Is it not already written "You shall not rob"? What, then, is the intent of the above? We are hereby taught that one who removes his neighbor's boundary marker transgresses two negative commandments. I might think (that the same holds true) also outside of Eretz Yisrael; it is, therefore, written "in your inheritance that you shall inherit in the land." In Eretz Yisrael one transgresses two negative commandments. Outside of it he transgresses only one.

Tosefta (Nidda 2:7) Marrying a pregnant woman or one nursing another person’s child is prohibited because of  hassagat gevul 

Yerushalmi (Sotah 4:3) A man should not marry a woman pregnant by another man or nursing another man’s child, but if he did marry her, the verse says about him: “Do not remove the eternal boundaries and do not enter the orphans’ field.” He who marries a woman pregnant by another man or nursing another man’s child has to divorce her and should never retake her, the words of Rebbi Meĩr, but the Sages say, he may separate from her and take her back later