 A couple things are going to happen. First of all, as you found out, Nicole, the water keeps coming back and back and back. The stain keeps coming back. It just leaks right through the finished paint. If you prime, that won't happen. But secondly, if you spot prime or maybe you just prime, let's say you have a two-foot square stain, if you prime that and nothing else around it, it's going to look different. You're going to see that patch, so to speak, in the ceiling because the absorption between the area that's primed and the area that's not primed