There's a thing called a Gish Gallop (all this is actually rather on topic for discussions of lying) where the counter to someone arguing your points, is to piv

There's a thing called a Gish Gallop (all this is actually rather on topic for discussions of lying) where the counter to someone arguing your points, is to pivot and rapidly throw out more points, pretty much anything you like, too fast to properly refute. It's a rather effective tactic for socially disabling an argumentative opponent: just not for anything truth-related. Might not be truth-related but it's still very real. All this relates to discussions of lying because the fundamental structure of the gallop, plus numerous other forms of BSing, requires the implication that everybody is in good faith: you're meant to grant that and then examine the arguments and see how they shake out. There's a lot of stuff happening in modern discourse where an anchor point to the argument is, 'since everyone here is in good faith and we just believe different things, let's break down the sides of the arguments'. But we're not. When you're desperate enough about winning (or not losing important things), good faith is disposable, and then people lie, for advantage, because they badly need advantage and aren't getting it from truth and good faith. Hence, the OP question of 'How can you tell if someone is lying?'. People will con themselves, but they will also lie on purpose to accomplish a goal.