"All" is an important indicator of sufficient and necessary reasoning. It introduces the sufficient condition.
"All Persian cats are pompous." All is describing Persian cats. Try to think of this as an if/then statement. If all of one group has a certain characteristic, then this characteristic is necessary. If it is a Persian cat, then it is pompous.
PC - - - -> P
Sufficient and necessary conditions don't always appear in the easily recognizable if/then format. You have to be able to recognize them even when they aren't. There are key words like "all," "always," "never," "only," "unless," etc. If you aren't familiar with these, you should watch the sufficient and necessary video lesson. Mehran discusses them in detail.