You notice someone in your team lacks the job-based competence that you would expect them to have. You can’t trust them to deliver to the standard required of their position.
A key consideration here is whether this is someone who is new to your team or to the organisation or whether it is an established individual who previously has been competent. Alternatively, it may be that you’re new to the team and you find yourself unhappy with the performance of someone you’ve been told is competent.
If it’s someone new to your team, you may want to reflect on the following points: