Ki Setzei: When in Love, Think Twice.
"You shall not plow with an ox and a donkey together."
Chinuch explains that the two animals pull at different rates, and one or both will suffer. Chinuch explains that this applies to human relationships as well. Two people with conflicting personality types should not become partners in a business nor in a marriage.
A farmer who is eager to get his plowing done may overlook the fact that pairing an ox with a mule will result in harm to the animals, and the loss will ultimately be greater than the gain.
We are vulnerable to infatuation, and this may result in failure to see incompatibilities.