Excerpt from my latest Sasstrology post (please leave comments on the Sasstrology site):
"When does a Scorpio not act like a Scorpio? Why would an Aries be different from what you expect? If a certain sign or house in their chart is emphasized, that energy will dominate. A grouping of natal planets (called a stellium) puts so much energy in one sign that their Sun can be overwhelmed (if it’s in a different sign). Or, if the house their Sun is in contradicts that sign, they may act in a way that’s not “typical.” If you rely on the Sun sign rules that a Scorpio is always intense, or that an Aries always wants to be first, you’ll find that you’re attempting to have a relationship with a very different person."