Every network packet that firewall handles can be input, output or forwarded. In relation to this, we have the three predefined chains that handle the entire network traffic. We make a list of rules that allow or block specific traffic.
Over time, our list can grow. At one point, we may have a list with several hundred rules. Mikrotik routers can have a long list, still to operate without problems. However, each netwrok packet must be respectively compared with each rule in the list until it finds appropriate.