The simplest and most general type of psychological motivation revolves around acceptance and love. Human beings are social animals, and even our fictional creations seek relationships and affection. For the most part, the crew of the Enterprise is presented as a surprisingly well-knit and supportive work place considering that initially most of them are strangers to each other. However, there are tensions that pull the characters away from each other, a reoccurring theme in first season "character episodes."
Sometimes you can almost guess what's written on each index card for the main character's motivations. Tasha Yar: gain measure of peace with troubled childhood. Worf: reconcile Klingon background with human upbringing. Wesley: stop getting treated like a kid.
Data is the character with the most obvious tensions over acceptance and one of the clearest character arcs over the course of the season. Even more than the truly alien Worf, Data represents a challenge to his friends and crewmates. Data simply does not get people and his attempts to blend in typically serve only to highlight this point. Very early on in the awful "Code of Honor," episode, Data attempts to tell LaForge a joke, failing spectacularly. A running gag in the first season is Data initiating a conversational info dump only to hear, "Thank you, Data, that's enough." By the second season, even the main computer gives him lip.
Data as a character really defines why I prefer looking at the needs of a character over situational conflicts (man vs. nature, man vs. man, etc.) What makes Data interesting, even early on, is this bottomless need to fit in paired with an utter inability to do so. Watching this 25 years ago, I initially figured this part of Data was a programming defect until the "Datalore" episode when it's revealed Data's incomprehension of basic human customs was feature not flaw. Data's creator intentionally created an imperfect android, one less offensive to the other human colonists of his homeworld. The other android created by Noonien Soong, Lore, tells the crew that the colonists grew alarmed by his more sophisticated understanding of human behavior. Although this phrase isn't used, Data is an example of the uncanny valley effect. The closer an android gets to being human, the more jarring the minor difference remaining become.
Actually, in retrospect, "Datalore" functions as a reboot for the character, the true beginning of his quest to be more fully human. By the end of the story, Data doesn't even seem to understand the betrayal that Lore's actions represent. To Data, Lore is a threat and once dealt with, Data continues on as before, alone but incomplete.
A better signpost to where the character is ultimately going happens later in the season in "We Will Always Have Paris," and "Neutral Zone," the season finale. Data has a pivotal role late in the earlier episode, beaming down to a computer lap and patching a flaw in time with a canister of anti-matter. Picard orders him into the risky situation because Data seems to be less bothered by the 'temporal hiccups' caused by the rift. Data, however, at first assumes the captain is sending him down because he is somehow expendable. Patrick Steward is able to provide Picard a moment of being taken aback by the android's clinical observation, a moment that Data seems to pick up on. Later on in the episode, three distinct Data's appear after another hiccup, with only one in proper phase to repair the rift. One of the android's calls out for the captain but it's the middle one that steps forward with a simple, "It's me!" The episode doesn't make a big deal out of this moment, but I actually like it a great deal. It's one of the first clear moments where Data expresses something like an emotion, first confusion and then the exhilaration of self-discovery. Not to beat a dead horse, but this is Data giving himself the measure of acceptance and recognition absent from the other characters with exception of LaForge.
Which is why Data's side-plot in the season finale strikes a chord with me. It's Data who beams over to the decaying satellite and rescues the freeze-dried 20th century passengers. Ryker and Picard seem repulsed by the survivor's behavior and attitudes but Data seems to identify with them. It's Data who forms a bond with the musician and seems genuinely tempted, or at least curious, by L.Q. "Sonny" Clemmons' offer in the closing scenes. Sonny offers something that Data had not realized he wanted, companionship and the casual acceptance of another. These are themes, obviously, picked up and elaborated on through the run of the show.