Imagine a bridge over a river, on one side you have 1000 people that need to cross it to the other side. If all of them cross it at the same time, it is possible, but it will take longer to cross due to room space and it will be a mess, giving chance for accidents. But you have a problem: there's injured people, eldery and children amongst them, what will you do in this case? Just create lanes on the bridge separating the injured, eldery and children so they can cross it calm and safely. The rest of people will cross it normally through its own lane.
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