[SteveSarre]

When the engine is cold, the injection system adds extra fuel to the mix.
(Which is what the choke does on older non injection engines). That makes it easier for the spark to ignite the air/fuel mix.

As the distributor cap, rotor arm and spark plug wires deteriorate, they become less able to generate and to pass a strong spark to each cylinder.

As spark plugs deteriorate, the electrode gaps increase and that also makes it more difficult for the spark to jump across and ignite the air/fuel mix.

When the engine warms up, less extra fuel is added, and you may reach a point at which the spark doesn't ignite the mix correctly. When that happens, you feel the engine misfire and lose power.

All because the ignition components had deteriorated.