The opening section of Parshas Re'eh formulates the principle of bechira chofshis (freedom of will). Although the Rambam has not listed this among what he considered the thirteen principles of our faith (ikarei ha'emunah), he clearly considers it an ikar (Rambam Hilchos Teshuva 5:3). Perhaps he has subsumed it under the eleventh principle - reward and punishment - because if man had no freedom of will, he certainly would not be held accountable for anything he did (ibid 5:4). The navi Yirmiyahu (9:22) tells us that no one should be proud of his intelligence, his strength, or his wealth, since these are all determined before a baby is born (Talmud Nidda 16b), and don't necessarily indicate greatness of the individual. However, yiras shomayim is up to the individual and is not predetermined. Judaism absolutely rejects the position of some psychologists that all decisions that anyone will make throughout their lives are predetermined, as if all of our decisions and reactions conform to a computer program encoded within our minds. We were told by Hakadosh Baruch Hu Himself that we were all created with the power of bechira - free will. This is the meaning of tzelem Elokim. Just as He created the entire world yesh me'ayin, so too he gave us the ability to make decisions yesh me'ayin. There are various considerations we keep in mind when making our decisions, all based on our psychological predisposition. But the final decision still remains up to us; our minds are not programmed in advance to make any specific decisions. All of our decisions are included within the statement of the rabbis (Berachos 33b) that all aspects of the human composition are predetermined (eye color, height, looks, etc.) except for yiras Shomayim. We are constantly bombarded by psychologists' theories that contradict this ikar of emunah, and we must realize that these theories are against a principle of our faith and are wrong.
It is interesting to note that when the Rambam formulated this most significant principle in Hilchos Teshuva (at the beginning of chapter 5) instead of referring to freedom of will as bechira chofshis, as it is commonly referred to, he calls it "reshus". In one of his drashas for aseres yemei teshuva, Rav Soloveitchk suggested that perhaps the Rambam meant to bring out the following idea: in modern Hebrew we refer to the elections as "bechirot". At election time, we are presented with a fixed set of candidates (or parties) and we choose from among them. Man, however, not only has "bechira chofshis" to choose from among the various options which are presented to him, but he even has "reshus", i.e. the ability to choose a path in life which was never even presented to him as an option. Therefore, even people brought up in a totally non-observant family and in an anti-Torah society also have the ability to choose - similar to yesh me'ayin - to be observant.
The Rambam writes (ibid.) that bechira chofshis is what distinguishes man from the rest of creation. Some people have the attitude that exercising their bechira to its maximum is the greatest demonstration of the uniqueness of man, so therefore the decision to sin and act against the Divine will constitutes the highest form of humanity. We sometimes enter an office and ask a secretary to take care of something for us. In order to show us "who is boss", the secretary will often give us a hard time. Similarly, people who serve in a supervisory capacity will sometimes refuse to grant requests to show us "who is boss". In both situations, control can equally be demonstrated in a positive and helpful way, i.e. by showing that it is within one's power to address the requester's needs, instead of a negative way. Unfortunately, many people have the flawed attitude that the stronger way to demonstrate one's power is by being negative.
The Talmud (Kiddushin 31a) tells us that one who does a mitzvah he is obligated to perform receives more reward than one who volunteers to do a mitzvah which is not required of him. Tosafos explains this based on a simple psychological principle, as follows: everyone likes to demonstrate his independence. As such, when one senses an obligation to do a mitzvah, a natural reaction is to refuse to comply to demonstrate his freedom and independence. Therefore it's more difficult (psychologically) for the one who is obligated to fulfill the miztvah than it is for one who is not obligated, and the reward for mitzvos is given in accordance to how difficult it was to fulfill the mitzvos (Avos, end of chapter 5).
However, there is a positive way for an individual to demonstrate his freedom and independence with respect to mitzvos. Let him not simply follow the commands of Hashem, rather let him do "his own thing" by volunteering something which is above and beyond the call of duty - lifnim mishuras hadin. From the body of the mitzvos which Hashem has commanded us (i.e, from the letter of the law) we can deduce what is the spirit of the law. Having once understood the spirit of the law, we can then choose to voluntarily implement that spirit in a way that was never even presented to us in the letter of the law; we can thus demonstrate our uniqueness and our tzelem Elokim in this most positive, meaningful, and sensible way.