So here's the misunderstanding, people think they're giving each other good luck, or at least wishing it...
That's not how I was taught, in fact that kind of thinking as criticized because it makes no sense and it really diminishes the dedication.
I was taught that dedication of merit is similar to maybe dedicating a hospital to the sick, like saying, " I do this good action for all of you and to further what good can be done."
So say you do your sadhanas, recitations, meditations, or talks, then at the end, you state what you're doing it for and what your aim was.
Stating your aim in itself, making it clear in your mind, makes you much more able to do good things in the future, it causes your good qualities to grow.
So anyways, that's what I was taught, maybe now you can dedicate merit without having doubt because it doesn't make sense.
Understanding it as good luck is still a noble belief, though. If a person does think of karma as "luck," and thinks they're actually taking away their own luck to give to another -- that's a delusion, but a very compassionate and noble one.
Christians take the view, "Jesus was God in human form, came to us, and died for our sins." Muslims take the view of Jesus as a prophet, Muhammad as his prophet, and revealed the Qu'ran. Hindus have even more complex mythologies of great cosmic beings and energies, in a vast inter-dimensional story.
...All of these are merely views. But despite that, each of them can use these views like a hammer: they can use it for violence or for compassion. If they use it for compassion instead of violence, what is the problem? It is better that they penetrate the view to find emptiness, but filling the heavens and emptying the hells is second-best.