It doesn't matter if it's unknown, it's related to chaos theory, look into that if you want. Basically if you take an extra little bit of cereal in your bowl you'll take an extra bite, take an extra few seconds to get in your car to work, you'll just barely not make the light instead of make it, and end up being on the train tracks when the train comes. But you didn't know it at the time. It's also possible that the extra bite kept you back and saved you from being hit by the train. The point is everything we do impacts us, but when it impacts us in a neutral and unknown way, it doesn't matter. So if the deck is continuously shuffled or if it's determined like a real life deck, it doesn't matter to you. Sure if you had taken an extra second you could have hit your royal flush, but it's also possible taking the extra second will cost you getting your royal flush.
Burn cards are to make sure people can't see the top of the next card to come, which would allow for marking the deck or even just observing natural differences (say the A of spades had a ticked edge or something, of course if this is true with the burn card people can now know which card is NOT coming and which card is NOT in anyones' hand, but that's better than people knowing exactly what's going to come before the betting).