There are $3$ types of sandwiches, namely chicken (C), fish (F) and ham (H), available in a restaurant. A boy wishes to place an order of $6$ sandwiches. Assuming that there is no limit in the supply of sandwiches of each type, how many such orders can the boy place?
I know that this is a stars and bars problem and the solution is $8 \choose 2$. But why can't it simply be $3^6$ where each of the $6$ sandwich places has $3$ choices to fill as repetition is allowed. I know I am missing something trivial.