Roosevelt and Hoover had night-and-day differences in personality and political skills, but both deserve failing grades in economics.

FORBES: Fact and Comment

They are interesting because this is the first time that differences in personality have been shown in wild birds.

ECONOMIST: Animal personalities

"Whereas personality similarity is likely to facilitate this process, personality differences may result in more friction and conflict in daily life, " she said.

BBC: NEWS | Health | Similarity 'makes happy marriage'

The results, published this year in the journal Personality and Individual Differences, didn't bode well for pickup line devotees.

FORBES: The Ten Worst Pickup Lines

After that, though, the personality differences manifested on a daily basis, eventually ending in a standoff and legal battle that devastated both sides, but somehow preserved the business, at a great personal cost.

FORBES: Six Crucial Questions To Ask When Picking A Business Partner