just last night, on my second cook ever on the performer, I lit my coals in a basket, got them all white, dumped them out, spread them over the bottom grate, and started adjusting my vents.
It was running up around 500 and I wanted it to settle in around 450 so I closed the bottom a bit, without much temp difference, so in my infinite wisdom, I closed the top about 3/4/ the temp fell, an I thought I had it dialed.
I put all the food on, replaced the cover, and waited for it to come back up to temp.
never happened. At least half of the charcoal went out from me apparently closing the vents on the bottom more than I thought and closing the top as much as I did.
Only one little portion stayed lit.
I had the entire family here for dinner, and I had to finish it in the oven, I simply couldnt get that grill going again (with all the food on it).
Lessone learned, adjust the vents and watch like hawk with the lid closed till you are happy with the temp....then put the food on
And mark your slide somehow so I can tell where the vents really are.