How come this always happens?

Part of growing up is finding out who you are. You dont have to know who you are, you have so much time to figure it out. you're likes and dislikes will always change, that's something you cant help. Dont stress, you'll find out who you are one day! Stay strong. :)

Looking back at what you've done in the past and being ashamed is - I think - pretty normal. I remember all my past projects with so much pride, and when I finally view them again, I realize I had nothing to be proud of.
That's why I usually try not to look back on them, but just remember how I feel about what I did.
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Now, not being satisfied with any choice you made, being unable to make a decision because you always feel it's crap, that's something that I feel too and that I attribute to my perfectionism as well. I'm not able to pick a template for a PowerPoint presentation, I always wear the same colours because I feel nothing else fits me, ...
I would argue that this is not a problem. It makes us more picky, more critical of ourselves, but that increased sense of observation and opinion, even if it leads to dubious artistic choices, forges us and gives us a unique style.
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I am 22, and for the past 5 years I haven't had a favourite color, animal, food, etc. When I'm asked, I usually use the answers I gave when I was a child. I still say that my favourite animal is the tiger, but I think about tigers once every year, and that's when I'm asked what my favourite animal is.
As we grow up, we learn not to pick things in particular, but to mix opinions, styles, and to explore more and more. We become more versatile, more open, and what defines us isn't a set of discrete values, but a gradual tendency described by our actions and thoughts.
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Remember that there will always be people better than you at anything, but also people worse than you. If you compare yourself to others, you are bound to be biased, and this might lead you to underconfidence or overconfidence. Believe in yourself, but also try to beat yourself. Because you are your only real competition.
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I like your style of writing, very neat, very organized. Don't say you are a failure, because you let some negatives outweigh the various positives you are taking for granted.
And trust me, perfectionists are far from being perfect ;). Have a good one!