Ben biliyorum ki Kamil hayatında hiç sevişmedi.

In English when we make sentences with never or ever, it automatically refers to the subject's total experience. Like when we say "John never kissed." It automatically means that John has never touched lips with another person in his entire life. But in Turkish, when we say "John hiç öpüşmedi.", it sounds as if the sentence did not end yet, as if it would continue with something like "at the party" or "on that boat-trip". So we put "hayatında" (in his/her life) to emphasize this point. Additionally, depending on the subject, it would conjugate as "hayatımda, hayatında, hayatında, hayatımızda, hayatınızda, hayatlarında".