Effectiveness is related to both Radical Acceptance and Wise Mind. Radical Acceptance and Non-Judgmentalness skills help us approach situations without getting emotionally involved or judging them. In doing so, this allows us to use Wise Mind to proceed effectively. In DBT, when we use the term effectiveness, we are talking about the skill of approaching the situation based on what works, rather than what's right or fair or any other judgment. It means taking a step back from the situation and deciding based on what works for you rather than on stubbornly insisting on things being fair or right. If a genie granted me wishes, I'd wish for the world to always be fair, but until that happens we all need to accept that unfortunately life just isn't fair. All we can do is acknowledge that and work to make our lives as good as possible in an unfair world.
For example, if you have a disability that makes it hard for you to watch a movie with subtitles, but someone you're watching a movie with finds subtitles distracting to the point of not being able to watch or enjoy the movie, how do you handle that? You might think that because you have a disability, the other person is "wrong" in this scenario and should accommodate you by using subtitles. The other person likely thinks they're right, though. To them, they can't concentrate on the movie if the subtitles are there. Ultimately, if you decide to push the issue, you may damage your relationship with this person by making them feel that their needs or ability to enjoy the movie aren't important to you. If you value this relationship, then no matter how much you may be in the right, you might choose to find compromise and prioritize your long-term goals to keep this relationship healthy by finding an activity other than watching a movie that you can both enjoy and participate in together.
Even if the other person is objectively being unreasonable, standing your ground and insisting on what's right may lead to unwanted consequences. For example, if you're working retail with unsupportive management and a customer is screaming at you, yelling back may get you in trouble, cost you your job, or cause the confrontation to escalate to physical violence impacting your safety. While you'd be in the right and in an ideal world nobody should ever treat you that way, you can't make other people behave. You can only control yourself. Acting effectively would mean doing what you need to do to get through the situation and prioritizing your wellbeing and safety.
Effectiveness doesn't mean you should always cave or let other people walk all over you. In many cases you should stand up for yourself and assert boundaries in a healthy way. Being effective requires that you decide when (and how) to cave or to stand up for yourself based on what actually works, and not based on how you want the world to work. While you might cave on something that isn't that important to you or where an acceptable compromise exists to preserve an important relationship, you might insist on having your needs met when preserving your relationship with the other person and being able to continue to get along with them is less important to you than what you're disagreeing about. You should also consider your moral values when deciding what is effective. Something is likely not effective when you have to compromise your moral values in a way that will leave you less able to respect yourself or that you might regret.