Each individual's personality is different. I know of a very sentimental collector who has kept all his watches starting from lower secondary school up to present so you'll see Timex, Seiko, Orient, Citizen, Titonis, Favre Leuba, Mido, Heuers, G-Shocks, Omegas, Rolexes up to present AP, JLC, IWC, etc..
In my early years I used to do that. However over the last 3 years, I've made yearly resolutions to reduce whatever I had from 30+ to 20 and presently down to 10. (I'm referring to whole working watches not those which may not be worth repairing and not saleable.)
Of course we will keep those very sentimental watches if we are lucky enough to receive a family heirloom like from our dad or immediate family.
I've always maintained that in my last 30 years of buying watches yearly, my tastes have changed tremendously over that period. I used to love certain brands and it was partially due to the marketing impact they had on me due to magazines, advertisements in the movies, etc..
As years went by and as I matured in my own marketing profession, I began to be able to separate the chaff from the rice, filtering out what was fact from created fiction. Many of those watches have since lost their attraction to me.
Nowadays, I don't read or pay attention to advertisements. Instead I research horological items online and seek out quality in movements and finishing without any preference in brands although at the end of the day that particular targetted watch must ultimately look good on my wrist.
I won't be surprised that 10 yrs down the road my current batch of watches might lose their attraction and I may lust after different watches in terms of size, complications, materials, industrial manufactured vs artisan-made...etc.
I'm not a sentimental person in keeping my old watches from schooldays to present. I've sold all those watches that I stopped wearing over the last 2 years some at dirt cheap prices.
Over all this time I realised time and time again that whatever collection or no matter how many I had at the time, I would always have only a few favourites that keep ending up on my wrist and others being relegated to the watch box for display only. So at this point in time I've decided that I should pare whatever I have down to only 7-8 watches which will end up being worn instead on being kept in boxes.
Perhaps I should sell one of my now empty watch boxes after the last few months of culling otherwise it may be tempting to fill it up again on impulse buying.
I do not think anyone is capable of selling everything and keeping only 1 watch not even if its a FPJourne, Kari V, Roger Smith, Urwerk, De Bethune,Richard Mille or PP.. we definitely need different watches for different situations and different moods..
Formal, casual, sports, travel.. as for me, I'm still trying to identify my current grail for each of these categories..
I've only achieved 2 so far this year.
Even as we achieve greater financial freedom, our targets keep moving higher and higher...
to have a watch in those 4 categories above coming from only AHCI's may be the ultimate nirvana, I guess...