Cancer · Scorpio
Two people who feel everything, and neither of whom will go first.
Cancer and Scorpio are both water, at an easy angle, and they are routinely sold to each other as the best match in the zodiac. They are extremely comfortable together. The problem with this pairing is not conflict. The problem is that nothing forces either of them to say anything.
What pulls
Neither of them has to explain themselves. Cancer does not have to justify why a tone of voice ruined the whole afternoon. Scorpio does not have to pretend an intensity that has frightened other people is not there. Being understood without translating yourself first is rarer than being wanted, and both of them recognise it immediately.
Where it grinds
Here is the part the compatibility charts leave out: an easy angle produces no friction, and friction is what makes people speak. Both of these signs wait to be understood rather than stating the thing, both of them withdraw when hurt, and both of them read withdrawal as confirmation. So they can sit in a silence that neither of them chose, each waiting for the other to reach in, for a remarkably long time.
The long version
This pairing does not usually break. It calcifies. Two people who love each other and have stopped saying anything difficult, on the grounds that they should not have to. The way out is unglamorous and entirely learnable, which is to say the thing out loud before it becomes weather. And it is worth knowing that a hard aspect somewhere else in the two charts, the kind that is supposed to be bad news, is very often the thing that saves this one.