My additions:

You're telling them what they already know - For constructive feedback to actually be feedback, it has to have a little bit of novelty. Either the feedback itself, or the giver's perception and experience of the situation that led to the feedback, needs to contain new information for the recipient, otherwise it's a lecture.

You can't stop talking - Once you've given the feedback, anything beyond that is... not feedback, it's something else. Maybe it's your role to go further, maybe not. Be honest with yourself about what you're trying to get out of the interaction.