The phrase "I mean" doesn't have a strong meaning of its own. Instead, it shows that you're expressing your feelings about a topic.
One of the reasons to use "I mean" is to try to get the listener to sympathize with your feelings and what you're saying. Because "I mean..." emphasizes that you're stating your own personal feelings, it seems like you're asking the listener to understand those feelings.
Here's another example. You would say this when talking to your boss:
I really think I'm ready to take on more responsibility. I mean, I've been working there for over six years. It's not like I'm inexperienced.