I always say that entering interviews with a balance between confidence in your relevant skills, yet humble to future possibilities is the way to go. A "confident humility"--if you will.
It is critical to assert yourself, and exude confidence in your responses about your previous experiences, transferable skills, and motivations for applying. If you're not secure in your work, how can a possible employer feel secure in hiring you?
However, overcompensating how successful or accomplished you are may veer into arrogance, which can be undesirable and unappealing for employers (and others). Thus, humility is a critical aspect of human relations, interviewing, and life! We are all human after all, and perfection doesn't exist--so we may never fully be aware or have control of future obstacles that may arise in a potential project, assignment, or mission within a company. Thus, balance is key.
Let's try an example: "Tell me about a time you reached a big goal at work"
This question doesn't simply ask about the triumphant destination of this goal, but rather seeks to reveal how you dealt with & overcame challenges. It seeks to understand the humanity of the interviewee. Were there interpersonal/relational conflicts on your team? Was your project on a tight deadline? Did you learn something new about the work--about yourself?
This is your chance to share your non-linear, yet personally fulfilling and professionally successful journey to this big goal.
Now, lead with confident humility my friend! Onwards.