assertive communication in the practice of project management

Assertive behavior is best always since it involves Emotional Intelligence. E.Q also means understanding our own emotions/understanding others feelings and emotions and communicate/express accordingly!

Thanks, emotional intelligence is an important component of assertiveness but is not the only one. communication skills are very important too.
Another aspect is the maintenance of self-control and maintaining "inner serenity".
what do you think about it?

yes, probably i didn't use the correct expression, I'm sorry but English is not my maternal idiom (would be better in Italian :)). I try to explain in other manner.
Self control is matter to control our sentiment or, in other therms, is the "action" to control, block our real sentiments. The external elements provoke an emotional reaction which we control: our behavior is not expression of our real sentiment .
Inner serenity is the sentiment.
My affirmation is: assertive people don't react against the behavior of the other part but maintain the control (self control). At the same time they act and express clearly their interests and needs not having influenced the sentiments by the situation because they act in harmony with their principles.
hope now is more clear
thanks

I am with Fosco on this one.

Assertiveness is the ability to state your point or argument, regardless of the other stakeholders point of view.

The trick is in not crossing the line from being assertive to being aggressive.