I know in my own case, I have been through all the mentioned stages. Starting breast development at 14, having breasts is all I know. Having the movement, weight and projection off my chest is all I know. I have had my breasts so long now, if they were removed, I wouldn't know how to react. I would definitely miss them. My breasts are now a part of who I am. I now understand why women are devastated when they have to have a mastectomy. That has not been always been the case though.
Certainly in the shame phase during my teen and college years, I would have given anything to have had a flat chest like the other boys who seemed to be dating girls rather easy. Very few girls were even interested in me and the ones who were only wanted to know about my breasts. Usually one date and they were satisfied. Which led to embarrassment knowing those girls were talking about me among themselves. Knowing men don't have breasts, it was something to hide. In those days I was a B or C cup and getting harder to hide my chest, even though I tried and tried. What made it harder was my breasts were fairly perky in those days as well. I have come across pictures where I am noticeably slumping to try and hide my chest to no avail. In my late 20's I began to yo-yo diet putting on weight to try and hide my chest. All this did was lead to more fat being deposited on my chest and hips. Not dissimilar to women when they put on weight, a byproduct of the elevated estrogen in my body. Fat that is still there to this day which is why I am a DD/DDD size, but without the perkiness. Eventually, I started to tolerate my chest since I had no choice. Later, I had a couple of bouts of boob rash under my breasts in my IMF. During one of those bouts I had also begun a supervised weight lose program. I spoke with the LNP assigned to me about what to do. After a lengthy conversation, she suggested I should consider wearing "chest support" to lift my breasts off my chest and to reduce movement to help reduce the chance of irritation that could cause a rash. At this point, I reluctantly began to accept my chest. I fought it for a little while longer, but after losing about 40 pounds, there was no reduction in breast size. Even after 100 pounds lost, my breast still remained the same size. I eventually bought a sports bra and found it was life changing during exercise. I started to treat my chest for what it is, glands and fat. After a short time, I started wearing a bra full time and that led me to a fitting. Which added additional confidence and comfort as well as appearance with a bra that fit me. The more I wore a bra, the more confidence I gained of my appearance.
I came to the realization that I couldn't hide my chest anymore than a woman can hide hers. I educated myself on bras and breasts and started to research tricks endowed women use to play down their chests with bras and tops and this led to a sympathetic appreciation and understanding of what women go through dealing with their breasts, good and bad, but that I, too, can appreciate and enjoy my breasts and not be ashamed. I have a much better understanding and appreciation and feeling for women due to my breasts because I was dealing with many of the same issues they were dealing with. It wasn't because they were women, it was because of having breasts. I completely understood. I have many of the same frustrations with my chest. I am sure some of that is due to the estrogen, and some is due to what you do when you accept your breasts that is similar to the same as women do with their own breasts.
But it has taken many years and many experiences to get to this point. I just came to the conclusion it was just easier to deal with my chest for what they are, breasts. And that has made all the difference for me.