Whenever I give talks I usually put in a few slides about grease. In discussions on this topic, questions mainly fall into three areas.
The first is why is it so critical to use only the grease that is approved for a certain application. A lot of people think grease is grease, so they should be able to use whatever is available.
An important point to remember is that grease is not really thick oil. It is base oil that has a thickening agent mixed in, much like my mother would mix corn starch into thicken the gravy.