Not harder to burn.. it is more resistant to self ignition.. so that it does not prematurely detonate before the spark plugs ignites it. Once the spark plug fires and there is a source of ignition, the RON 100 will burn just like any other fuel.

Harder to burn WITHOUT ignition source. Once you light it with spark, it burns like lower RON fuels. The harder to burn part does not matter when there is an ignition source. Cars that don't need premium fuel might get less power is not because the fuel is harder to burn but higher octane means more 'hydrocarbon' addictive added to the fuel and the fuel no longer produces the same amount of energy. The fuel still burns but produces less energy than a lower RON fuel. Maybe in other languages they use the word 'harder to burn' as to say it produces less power. If that's the case I don't speak the other languages so well and won't argue with you on that.

He is coming from the point that they have to put more hydrocarbons in it to up the RON.. which is also why higher RON petrol does not produce the same amount of power as lower ron since there is 'more' hydrocarbons per part of fuel.