Double effect distinguishes intending harm, including harm used as a means, from foreseeing harm while pursuing a good end. Traditional formulations also require a permissible act, a sufficiently serious reason, and limits on how the good is achieved. Calling something a side effect does not alone establish permission.
Intention concerns what an agent adopts as an end or as a means of achieving it; foresight concerns what the agent expects to happen. Regretting a harm does not automatically make it unintended if the plan depends on producing it. Conversely, a foreseeable harm can remain a side effect. Traditional formulations also impose conditions on the act, the means, and proportionality. The distinction therefore offers a structured argument, rather than a general excuse for unwanted consequences.