What Causes the El Niño Southern Oscillation?

There's a lot of explanations of what El Niño is and the consequences of it's occurrence. But few if any resources adequately tackle how it occurs in the first place. What would compel the ocean to act against this positive feedback loop? What causes this positive feedback loop in the first place?

To answer these questions we must look at how fluids behave on a rotating sphere and how that influences the thermocline.

Sources:
The El Niño-Southern Oscillation Phenomenon - Sarachik, E. & Cane, M.

El Niño and Southern Oscillation (ENSO): A Review: https://doi.org/10.1007/978-94-017-74...

Mechanism of Kelvin and Rossby waves during ENSO events: https://doi.org/10.1007/s00703-002-05...

Charging El Niño with off‑equatorial westerly wind events: https://doi.org/10.1007/s00382-015-28...

Higher frequency of Central Pacific El Niño events in recent decades relative to past centuries:
https://doi.org/10.1038/s41561-019-03...