I have been meditating (samatha-vipassana within the Theravada tradition) for many years now, and I see myself always falling in the same pattern:
(1) I have periods of very high motivation, which can last 2-6 weeks, and in which I make lots of progress and develop good levels of insight and concentration (good access concentration, experiences of pity and sukha, more lucid insight on impermanence, etc.) I also read and watch lots of content on practice and get closer to people who share this "interest".
(2) When these phases wane, my sittings get increasingly filled with thoughts related to other life matters, especially things that demand high levels of engagement and to which I am somewhat attached (work projects, a new hobby, a new life development). I keep my regular practice (2hrs daily: 1hr in the morning, 1hr in the evening) but my concentration quickly decreases, and I struggle to stay with any object of meditation for long periods. Mindfulness in daily life also gradually disappears.
(3) This goes on until a reading, a conversation, a film or something apparently random brings me back into state (1).
Going through these phases, insight and understanding of practice is the only thing that very slowly accumulates, and gradually increases, but concentration and mindfulness really oscillate and always seem to get back to where I started, whenever I experience state (2).
I have observed this for many years, with many eyes and from many viewpoints inside myself, while sitting and while mindful in action. And what stands out to me is a certain quality of motivation (for lack of a better word) which manifests as a cluster of perceptions, emotions, physical patterns and thought processes. This motivation (like the so-called dopamine cycle, to which it is probably linked) seems to go through a growth phase to a peak, and then decrease.
I have tried to voluntarily trigger the growth of this motivation factor during the descending phase (2), by reading books and create commitments that relate to the practice, even though obviously part of me develops aversion or neutrality to the whole thing. This has rarely worked.
How do you deal with motivation swings on a scale such as this? What can I do to change this pattern and boost my progress? Observing all of this does not seem to have much of an impact, at least so far.