10 Small Details You Missed In Tenet
3. The Grandfather And Bootstrap Paradoxes
As mentioned before, Tenet's approach to scientific accuracy is shaky but can act as a solid entry point into various fundamentals of physics.
Its approach to paradoxes is noteworthy, especially the Grandfather and Bootstrap ones, despite its glaring inaccuracy in its approach. The Protagonist even alludes to this while talking to Neil about how the Grandfather paradox essentially means that the plan by future humans to wipe out their ancestors failed.
Neil of course handwaves it by stating that it's a paradox, and therefore an eternal process. However, the movie ends with the world being saved despite the best efforts of Sator and his allies. This, of course brings up questions of free will, predestination and challenging fate, as well as a different kind of paradox.
Due to the Protagonist's knowledge and experience of these events, he knows to create Tenet and recruit Neil in the future, acting as an example of the Bootstrap paradox due to the causal loop of the Protagonist's actions.