Hey Rachel! So you bring up a good point: In the video with the examples discussed, we start with a reactant that is conjugated. Upon being protonated, for example, we get an intermediate, an intermediate that is resonance stabilized (and then the reaction proceeds and finishes). Once we’ve formed a product, we theoretically have the choice to react with the double bond in that new product, or another fresh conjugated reactant. If we assume we have 1 equivalent of reactant and 1 equivalent of reagent(s), the reagent(s) will react with a fresh reactant that is conjugated because the intermediate produced with be resonance stabilized (as opposed to the newly produced product which will have a carbocation that is not resonance stabilized). Nature does what’s most stable, so the most stable intermediate will be formed. If you have an excess of reagent(s) then every double bond in the original reactant will fully react. But, if you have a 1:1 reactant:reagent ratio, then it will proceed how it is discussed in the video. Does that make sense?