Excerpt from my latest Sasstrology post (please leave comments on the Sasstrology site):
"Sometimes a person’s planets combine with your planets to create (seemingly) insurmountable relationship challenges. But actually, that person is the missing piece of your puzzle. Case in point is if you have a natal T-Square: two planets in opposition, and both squaring a third (the focal planet). If your partner’s planet opposes your focal planet, a Grand Cross is created between the two of you. That’s a whole lot of tension (a giant square with two oppositions inside it). However, this is actually one of the stronger synastric connections."