What is an assertion, give an example?

Hint: The aim of assertion would be to persuade readers that they need not question or differ with what they hear or read, but rather grasp the concept or thought as unquestionable truth. It has proven to be one of the most effective ways for writers to directly put their opinions, thoughts, values, and ideas.

Complete answer:
A person makes an assertion when he expresses an opinion with a deep conviction in it, as though it were real, even though it isn't. Assertion is an artistic approach or strategy that involves making a powerful assertion, a compelling or confident and optimistic statement about a conviction or a fact.

Sometimes, there is no proof or evidence to back up their claims. Its aim is to explicitly convey thoughts or feelings, such as "I have made every effort to finish this task yesterday."

To state an example for an assertion consider a scenario: You are stating your opinion about the mistreatment of animals in a country;
The assertive statement would say: “I think animal cloning has to be banned in every country.”
Here the subject has taken a stand. This would denote that the person not only has an opinion, but stands firm to it and openly takes responsibility for what they have said.

Note: Apart from assertions if we take assumptions then it is a claim that the author makes without attempting to verify. To assume implies to take something for granted or without proof; to assume as fact; to assume or take haphazardly or tentatively. The author actually believes the statement is right instead of proving it.