While you don't have to know why it works this will be a quick explanation of why the double Zeal item BORK build works. To start with the core, BORK has a passive making you deal 8% of your targets health as physical damage on hit. It also has an active that allows you to debuff an enemy champion with slow, giving yourself more movement for some self peel. Next, the RH adds an additional 15 on hit physical damage, and makes your AA fire at two other nearby enemies dealing 25% of your AD and applying on hit effects (Can also critically strike). The second Zeal item is just for the AS and Critical Chance. This means that with every AA you deal 8% target current health damage to 3 targets, with all 3 hits able to crit. With all the items stacking high AS, allowing you to use this for all your damage. Note that you can also stack BC on top of this to shred 3 targets armor with every AA.