I do hear what everyone is saying about life experience, and I think I agree. But I did also want to add that no matter how experienced a T may be, they cannot possibly have experienced everything that each of their clients has experienced in life. They may be of a different ethnicity, or be in a different sort of relationship (e.g. married/not married), or they may have been divorced where their client has not and vice versa. That's without getting into all the more complex issues clients may bring to therapy: addictions, eating disorders, traumas etc. I'm sure we wouldn't want for T to have actually lived through every one of those difficult issues, personally.
I think there can be another kind of experience, as well as living through things yourself. on a personal level, where you think to yourself that you have a friend or family member who has been through or is going through something similar. And on a professional level, where T remembers that they have worked with other clients with similar issues before, and also perhaps that they have learned a lot from a mentor or supervisor who has worked with many people in a similar situation.