[iloaepdx] The clock waits

Lay out a digital circuit in a toy digital simulator.  You can see electical pulses traveling along the wires and logic elements you drew.  The system waits for all input pulses to reach each logic element before it fires, generating output pulses.  You don't have to make the wires all the same length.  (Of course, this is unrealistic.)  Sequential logic elements wait for all combinational logic elements to have completed the previous clock cycle, then the clock ticks.  You don't need to worry about meeting timing.

Maybe animated characters travel along roads, wait patiently outside the doors of their destinations.

Inspired by the difficulty of building computers in Conway's Game Of Life: one has to get the timing of everything just right.