Problems may also occur because you run out of ports.
Problems occur because Apple updated 2017 MacBook Pro models to use Thunderbolt 3 (USB-C) ports exclusively, while older Macs use a variety of display ports, including HDMI, Mini DisplayPort, and Thunderbolt 2, which aren't compatible with Thunderbolt 3 (USB-C) instead, different cables and/or adaptors are required. Buy or use a new MacBook Pro, and you'll likely encounter trouble connecting external displays using cables and adapters that worked well with older MacBook Airs and MacBook Pros.
