Kinesthetic motor imagery (KMI) generates specific brain patterns in sensorimotor rhythm over the motor cortex (called event-related (de)-synchronization, ERD/ERS), allowing KMI to be detected by a Brain-Computer Interface (BCI) through electroencephalographic (EEG) signal. Because performing a KMI task stimulates synaptic plasticity, KMI-based BCIs hold promise for many applications requiring long-term KMI practice (e.g., sports training or post-stroke rehabilitation). However, there is a lack of studies on the long-term KMI-based BCI interactions, especially regarding the relationship between intrapersonal factors and motor pattern variations. This pilot study aims to understand better (i) how brain motor patterns change over time for a given individual, (ii) whether intrapersonal factors might influence BCI practice, and (iii) how the brain motor patterns underlying the KMI task (i.e., ERDs and ERSs) are modulated over time by the BCI user's experience. To this end, we recruited an expert in this mental task who performed over 2080 KMIs in 26 different sessions over a period of five months. The originality of this study lies in the detailed examination of cross-referenced data from EEG signals, BCI data performance, and 13 different surveys. The results show that this repetitive and prolonged practice did not diminish his well-being and, in particular, generated a sense of automatization of the task. We observed a progressive attenuation of the ERD amplitude and a concentration in the motor areas as the sessions accumulated. All these elements point to a phenomenon of neural efficiency. If confirmed by other studies, this phenomenon could call into question the quality of the BCI in providing continuous stimulation to the user. In addition, the results of this pilot study provide insights into what might influence the response of the motor cortex (e.g. emotions, task control, diet, etc.) and promising opportunities for improving the instructional design of BCIs intended for long-term use.