Things are complicated. Whether it's a debate about whether to buy a dishwasher or who should be elected president, there are always anywhere from several to hundreds of relevant factors to be considered and weighed according to importance, based on whatever data is available and hopefully accurate at the time. No one has thoroughly considered all these elements and details beforehand, so when entering a debate it is hard to know which side to choose. However, if you think according to some guiding abstract principles, general ideas that apply to many situations, you can use those as a kickoff point when choosing what side of a debate to align yourself with, and if you started out with the right principle the details of the debate turn out to work in your favor once they emerge.
For example, suppose someone were to ask whether the government of China should regulate their carbon-emissions. Though seemingly simple, this is a very complicated question that most people have not previously considered. Without detailed knowledge about the true state of the environmental impact in terms of empirical scientific data; a robust understanding of the political and economic atmosphere of modern-day China and consequences; undisclosed details unavailable to the public about business arrangments and vested interests, conflicts, and unintended side-effects; a consistent philosophical framework about the tradeoff values of different options; etc. one can't even begin to claim sufficient knowledge to create a well-informed opinion. And to be missing just one, let alone the majority or all these components could diametrically change the ultimate conclusion. However, if one were to begin with the hypothetical principle that free enterprise generally produces the most efficient results, then using that as a startoff point they would choose "No, China's government should not regulate carbon-emissions," and then, when the details of the debate do emerge, they will conveniently end up working in your favor.
However, in the unfortunate case that the details, only evident at the end of the debate, turn out to work against you, the upside is that at least this allows you to re-evaluate and refine said principles, so as to be of greater use at some future event.