Then how does a discovery takes place?
"Has scientific merit" doesn't mean "is established science."
An idea that is consistent with observations without excessive complexity or real contradictions can be of scientific merit without being established science, and without necessarily being true.
Ideas of scientific merit only stay being of scientific merit if they are thoroughly tested, if they are actively attacked in a serious attempt to demolish them. This is science. Science submits ideas to vigorous trial by fire, so that ideas that survive can be trusted.
Pseudoscience is taking an idea, declaring it to be a good one, then proceeding to prop it by any possible means and denying any flaws that others might find.