the sun is bright is a fact, its self evident that anyone who can see the sky can see, if that is you example it is a poor one. 'you exist' well that is also self evident, this argument wouldnt be taking place if i didnt. a source doesnt need to be a peer reviewed study, it just needs to be anything you can point to. I could argue that the sun isnt bright but all you would need to do is point upwards. Maybe if you were talking to a person who has lived his whole life in a cave you might need better evidence than it being self evident, you could tell him to exit his cave to see and that would be enough, if they refuse to see for themselves then they are willfully ignorant. Both examples though you can quickly point to something to verify the truth so that both participants of the argument can be arguing over the same facts and to move onto the crux of the issue.