Ah, your talking about the cinnamon challenge, right?
There is a couple of reasons this is difficult to do and also not a good idea to try. Cinnamon powder is very hydrophobic (which means it doesn’t “like” water), therefore it is very difficult to mix with your saliva. Saliva lubricates our food and helps us to swallow it. Since it doesn’t mix the powder just coats the inside of your mouth and gets stuck there. Add to that the fact that cinnamaldehyde (the chemical in cinnamon) is actually pretty nasty at high concentrations so it stings the inside of your mouth and makes you feel pretty sick. Finally, and probably most dangerous, since you now have lots of a fine powder stuck in your mouth, when you breathe in you risk inhaling the powder into your lungs. This is really dangerous and makes you cough and splutter. Obviously coughing, feeling sick, having your mouth sting, and being unable to swallow all together makes it very difficult to eat cinnamon.