Due to the inherently competitive nature of living in a society that competes for resources, many people assume that a kind, upbeat person will be easy prey for someone tough and pushy. They lack the emotional intelligence to understand that you can be both kind and assertive.

In reality, you catch more flies with honey. Pretty much every study of game theory concludes that nice but assertive is the optimal strategy in any ongoing interaction. A nice person with a backbone is likely to be healthier boundaries, lower stress, and better relationships with people.