[This post is part of a series on Coaching Highlights from coaching Columbia Business School students. If you don’t see a Table of Contents to the left, click here to view the series, where you’ll get more value than reading just this post.]
As an earlier post in this series mentioned, assertiveness ranks highly as a skill students at Columbia want to develop as part of their leadership training. Most recognize it as an important skill for leadership — that if they don’t assert themselves, instead of leading they’ll end up being led by others who assert themselves more. Most haven’t had or created the opportunities to assert themselves professionally, having had few leadership roles.
I find one of their biggest hurdles to asserting themselves is misunderstanding assertion. Clarifying its meaning helps them a lot. I expect it will help a lot of readers here.
Assertion does not mean aggressive, domineering, or trying to convince. It involves you, not the other person. Most people recognize the problems and challenges of trying to change other people so hold back from what they think is asserting but is really asserting+influencing or asserting+domineering. When people mistakenly attach to assertion something involving others they increase their challenge to assert.
To assert simple means to communicate your interests and perspective. While you might at first think just communicating your interests and perspective does less than, say, also influence others to agree, just stating yourself goes a long way, often farther because you risk getting mired in disagreement less. Once you assert yourself you have the option to act on what you communicated — maybe to try to convince or influence, but you don’t have to.
Wikipedia puts it well, especially the part I bolded:

Assertiveness is the quality of being self-assured and confident without being aggressive. In the field of psychology and psychotherapy, it is a learnable skill and mode of communication. Dorland’s Medical Dictionary defines assertiveness as: “a form of behavior characterized by a confident declaration or affirmation of a statement without need of proof; this affirms the person’s rights or point of view without either aggressively threatening the rights of another (assuming a position of dominance) or submissively permitting another to ignore or deny one’s rights or point of view“.

Freeing yourself from how others respond makes assertion easier and more effective. You’ll likely find yourself able to speak more freely, encounter less resistance, and be more open to listening to others
All of the above applies no less to business school students who tend to be more assertive than the general population.

Another useful perspective

Another helpful perspective about assertiveness is that working in a team often makes assertion your responsibility. I was taught that studies find that teams produce better results when they have more diverse input. If you are in a team but not contributing your perspective, you’ll hurt the team.
This perspective risks making people feel pressured and obligated to contribute, which can discourage them, so I combine it with the next perspective and practice.

A useful practice and perspective

Students report one of their main reasons holding them back from asserting themselves is the fear of judgment, which most of us can identify with.
A useful way to bypass this hurdle is to depersonalize the ideas they assert. You’ve probably seen people practicing it. They say things like “I don’t know if this idea is crazy or not, but maybe we should consider it,” “I just had this idea, I haven’t had time to evaluate it, but what do you think about it,” or “This idea may be dumb, but it might have a kernel of value too.” When you preface a suggestion like that before saying it, you decrease the risk of them evaluating you. Their evaluating the idea and finding it lacking doesn’t affect you when you frame the idea as something you haven’t had the time to consider either, but your responsibility to the group forces you to reveal it rather than keep it secret.
If you don’t normally say things like that before sharing ideas, try them for the freedom they create. They can overcome your risk of being judged personally while giving you the chance to share your ideas. They aren’t the only way to do it, but they work.