How can we explain Beth's success from the perspective of Self-Determination theories? How did her motivational reasons impact her success? Did they change over time? Let's consider Cognitive Evaluation Theory and Organismic Integration Theory.

Cognitive Evaluation Theory offers three basic needs for intrinsic motivation: competence (our abilities and skills), autonomy (our personal agency), and relatedness (relationships with other people). Organismic Integration Theory offers us a continuum which has amotivation at one end, extrinsic motivation (external regulation, introjected regulation, and identified regulation) in the middle, and ends with intrinsic motivation (integrated regulation). 

For an overview of both theories, see (Reeve, 2009).

What was Beth's motivation when she decided to learn how to play chess? She was 9 year old when she saw Mr. Shaibel, the orphanage custodian, playing this game. And she got fascinated with it right away.  Of course, there was a genetic predisposition. Her mother wrote a PhD dissertation on mathematics (we see her burning it in one of the first episodes). Beth was also very good at math. But in addition to that, she had this incredible intrinsic motivation for learning how to play chess. She dreamed about it, she was absolutely fascinated with it. Nobody told her that playing chess is good (so no external regulation/introjected regulation). Quite the contrary. Mr. Shaibel's first words to her were: "Girls do not play chess." She also didn't perceive it as a part of her identity at first (no identified regulation). She just wanted to do it. She would stubbornly repeat over and over again: "Show me," "Let's play a game."  Until Mr. Shaibel gave in...

Later, playing chess became a way to gain confidence and competence for little Beth. She was invited to play a simultaneous at the Duncan High School. Her opponents were all high-school young men, and she bit them in 1 hour and 20 minutes. "It felt good. I've never won anything before," - said Beth to Mr. Shaibel, while finishing a box of chocolates.

Beth's passion about chess would also help her to build relationships. Through learning how to play chess, she gained a first friend and a mentor. Mr. Shaibel would become an important figure in her life, and she would become an important person for him. He was the one who discovered her talent and introduced her to the Duncan High chess club's president. He was the first one in the orphanage to acknowledge her strengths: "You are astounding." He helped her to believe in herself and helped her to get stronger. He was also the one who truly believed in her till the rest of his days. He gave her a sense of relatedness, which helped her to keep going.

Beth is holding a picture of Mr. Shaibel and herself. She has just learned that Mr. Shaibel had passed away. Please note how she put her hand on his shoulder, making a personal connection with him.

At the age of 15 Beth got adopted and started going to a public school. Soon she realized that her peers looked down at her and didn't want to include her in their circle. She was not dressed as nicely as they were (and she also was smarter than them). Once she realized that winning chess tournaments could bring her monetary prizes, she started using this money to buy nicer things for herself. This turned into a new motivation to learn how to play even better (extrinsic motivation). The money which Beth won allowed her to change her style and gain the confidence she needed to become recognized by her peers (relatedness). More importantly, it allowed her to become comfortable with herself. That's how intrinsic motivation also became extrinsic.

There is another aspect of motivation I would like to consider here. I would like to look at the connection between Beth's success and her addiction to different substances, such as tranquillizers, alcohol, and drugs. The substances which she took were not a source of motivation for Elizabeth, but they helped her to open her mind and become an unpredictable and creative player. However, the more successful she became, the deeper she was getting into her addictions. Eventually, she got to the point where she had to choose between her addiction and her success. This happened when her lifestyle prevented her from winning a match with the Russian Grandmaster, Vasily Borgov. Biting Bogrov was her ultimate goal, her biggest dream. Her desire to win turned into a motivation to overcome her addiction, change her lifestyle, and become stronger.

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To sum up, Beth's interest in chess began with pure intrinsic motivation to learn this fascinating game. Later, it started to provide her a sense of competence and autonomy. Winning money at tournaments and being able to buy nice things and travel turned into an extrinsic motivation to improve her skills. Through succeeding in the game and earning her own money, Elizabeth became an independent and strong woman. She started to make connections with people who had similar world view with her and started to make true friends (relatedness). And eventually, her passion and her motivation to succeed helped her to overcome her addiction.