Duties of the Heart says that your parnassah isn't dependent on a particular means. "One should not think that his livelihood depends on a particular means and that if these means fail, his livelihood will not come from a different means. Rather, trust in the Al-mighty, and know that all means are equal for Him." You will get what is decreed for you. You should choose for your parnassah a field that interests you. "One who finds his nature and personality attracted to a certain occupation, and his body is suited for it, that he will be able to bear its demands - he should pursue it, and make it his means of earning a livelihood."
Thus, aiming for a high paying field is not proper if you will not enjoy that field. It will not bring you any more money. Often, those who live the contemporary Litvish mantra of the world standing on Gemara, Gelt, and Guilt can't imagine doing anything but studying Gemara lomdus. Then they can't imagine the purpose -- for those who "must work" as they say -- of doing anything but the most lucrative business because one needs money to support Torah and one word of Torah, blah, blah, blah. All the nuances of life are lost in this dogma. It is not the proper way to approach things. Going for the money against your nature is the same as seeing your occupation rather than Hashem as the source of the money. "If one's livelihood comes through one of the means he worked on, it is proper for him not to trust in this source, rejoice in it, intensify in it, and turn his heart to it, because this will weaken his trust in the Al-mighty."
Working in the wrong profession can destroy a person's mind. Likewise, abandoning your dreams can destroy your psyche. The Rambam said, "Seeing that the maintenance of the body in a healthy and sound condition is a God-chosen way, for, lo, it is impossible that one should understand or know aught of the divine knowledge concerning the Creator when he is sick, it is necessary for man to distance himself from things which destroy the body, and accustom himself in things which are healthful and life-imparting." (Hilchos Deos 4:1) If you destroy your mind, you also will not be able to engage in spiritual pursuits.
All those who have eitzah, all those rabbis who tell people how to live, keep this in mind. Get to know the person who comes to you. What makes him tick? What is his nature? You don't have to divine it. Ask him and usually he'll you. If your practice is always to deliver the bad news, always to say no, always to say no you can't do it, you can't go there, if you deem your job to be Mr. Din, if like the old Marx Brothers song line "whatever it is I'm against it." know that you are going to ruin people. The result will not be more Torah study but less.
Duties of the Heart:
55 Since it has been clarified the obligation for a man to pursue the means for a livelihood, now we will clarify that not every man is required to pursue every possible means. The possible means are numerous.
56 Some occupations are easy, requiring little strain such as shop keeping or light work with the hands such as sewing, writing, contracting businesses, hiring sharecroppers or workers, supervisors.
57 Some occupations require hard physical labor such as tanning, mining iron or copper, smelting metals, heavy transport, constant travel to faraway places, working and plowing land, or the like,
58 For one who is physically strong and intellectually weak, it is fitting to choose an occupation among those that require physical exertion according to what he can bear.
59 He who is physically weak but intellectually strong should not seek among those which tire the body but should instead tend towards those who are light on the body and that he will be able to sustain .
60 Every man has a preference for a particular work or business over others. G-d has already implanted in his nature a love and fondness for it, as He implanted in a cat's nature the hunting of mice, or the falcon to hunt smaller birds, the deer to trap snakes. Some birds hunt only fish, and likewise, each animal species has a liking and desire for particular plants or animals, which G-d has implanted to be the means for its sustenance, and the structure of its body and limbs is suited for that thing. The long bill and legs of a fish catching bird, or the strong teeth and claws of the lion, horns of the ox and ram (i.e. for defense - TL), while animals whose sustenance is from plants do not have the tools to hunt and kill.
61 Similarly you will find among human beings character traits and body structures suited for certain businesses or activity. One who finds his nature and personality attracted to a certain occupation, and his body is suited for it, that he will be able to bear its demands - he should pursue it, and make it his means of earning a livelihood, and he should bear its pleasures and pains, and not be upset when sometimes his income is withheld, rather let him trust in G-d that He will support him all of his days. And he should have intention when his mind and body is occupied with one of the means of earning a living to fulfill the commandment of the Creator to pursue the means of the world, such as working the land, plowing and sowing it, as written "And G-d took the man and placed him in Gan Eden to work it and to guard it" (Bereishis 2:15), and also to use other living creatures for his benefit and sustenance, and for building cities and preparing food, and to marry a woman and have relations to populate the world.
He will be rewarded for his intentions in heart and mind to serve G-d whether or not his desire is accomplished, as written "If you eat from the toil of your hands, you are praiseworthy, and it is good for you" (Tehilim 128:2), and our sages of blessed memory said "Let all your actions be for the sake of Heaven (to serve G-d)" (Avot 2:12).
63 In this way, his trust in G-d will be intact, undamaged by the toiling in the means to earn a livelihood, as long as his intention in heart and mind is for the sake of Heaven (to do the will of G-d that the world be populated and built up).
64 One should not think that his livelihood depends on a particular means and that if these means fail, his livelihood will not come from a different means. Rather, trust in the Al-mighty, and know that all means are equal for Him. He can provide using whatever means and at any time and however He so wishes, as written "for with the L-ord there is no limitation to save with many or with few" (Shmuel I 14:6), and "But you must remember the L-ord your G-d, for it is He that gives you strength to make wealth, in order to establish His covenant which He swore to your forefathers, as it is this day." (Devarim 8:18), and "Not by might nor by power, but by My spirit, says the L-ord of Hosts." (Zecharia 4:6).
Duties of the Heart 4:4
32 And likewise workers, merchants, and contractors are under a duty to pursue their livelihood while trusting in G-d that their livelihood is in His hands and under His control, that He guarantees to provide a man (as the verse "who gives sustenance to all flesh" - PL) and fully provides for him through whatever means He wishes. One should not think that the means can benefit or harm him in the least.
33 If one's livelihood comes through one of the means he worked on, it is proper for him not to trust in this source, rejoice in it, intensify in it, and turn his heart to it, because this will weaken his trust in the Al-mighty. It is improper to think that this source will be more beneficial to him than what was predecreed from the Creator. He should not rejoice for having pursued and engaged in it. Rather, he should thank the Creator who provided for him after his labor, and that He did not make his work and struggle result in nothing, as written "If you eat the toil of your hands, you are praiseworthy, and it is good for you" (Tehilim 128:2).