Nobody has only one belief. To quote Daniel Dennett: “You cannot believe a dog has four legs without believing that legs are limbs and four is greater than three, etc.”.
So when you are arguing about whether a dog has four legs with someone on Twitter, for example, there might be many other hidden beliefs contributing to the argument that you don’t agree on, and neither of you would get to know all of them through online exchanges. That’s why arguing online is neither effective nor a good use of time - you should refrain from doing it.
Please excuse my scrappy illustration below 😉. Still, I think it explains the reasoning well.