Not a text boook explaination but easier to understand, higher octan fuel is less volatile, the optimum way for fuel to burn in an engine is the burn starts at the top of the combustion chamber when the spark ignites it and burn smoothly down the cylinder, lower octane with forced induction will cause pre ignition meaning the gas can ignite off the heat and the compression in the cylinder from the botton creating the explosion before the piston reaches top dead center (actually just prior to TDC) making the piston take the shock of the explosion on the up stroke and by doing that trying to stop that piston and force it back down the way it came instead of completing the rotation and going back down. 91 or 93 (whatever the highest you can get) is required for turbo cars.

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1999 Civic SI, Boosted and built, 12.67@112.

Gone but not forgotten.....
1998 Eagle Talon ESI, built and boosted 14.2@98
1992 Eagle Talon TSI AWD12.91@104
1992 Honda Hatch swapped and sprayed14.0@108