The thesis of the book is that the most effective and powerful leaders balance projecting strength and warmth.
If you just show strength, then you would potentially be seen as dictatorial, a micromanager, unapproachable, all work and no personality, and maybe even a tyrant.
And if you just project warmth, then you would likely be seen as wimpy, emotional but not intellectual/skilled, managing by friendship and not professionally, and not focused on results.
That's why combining and projecting a healthy balance of strength and warmth is effective in leading towards mission results, but also in being a "mensch" and caring for the people you work with.
You can't have sustained strong performance without a happy workforce.
And you can't have a happy workforce without strength to achieve meaningful work performance.
In funny, but in a sense Arnold Schwarzenegger is a good example of someone who combines the two.
On one hand, he represents the big and strong "Mr. Universe," and was able to play in numerous action movies, such as Terminator, Predator, Conan The Barbarian, and more.
At the same time, Schwarzenegger always had a warm, softer side and stared in comedies like Kindergarten Cop, Twins (as the intellectual twin of street-wise Danny Devito), and Junior (where he undergoes a male pregnancy!).
While no one is good at everything and it can be hard to effectively balance strength and warmth, leaders that master this can become the real Mr. Universe for their organizations and people. ;-)
(Source Photo: Left from Andy Blumenthal and Right from here with attribution to Eva Rinaldi)