Birthdays are sweet.

Sweet like the birthday cake;
Sweet like the excitement for the upcoming event;
Sweet like the wishes for a fantasy world;
Sweet like the new opportunities you open;
Sweet like the sight of seeing pictures of your old self and being proud of your growth.

Birthdays are bitter.

Bitter like the slightly hardened, days old cake;
Bitter like the lost of the childhood wonder;
Bitter like the feeling of never seeing your wishes come true;
Bitter like the loss of orientation in your goals;
Bitter like the sight of seeing pictures of your old self and wishing it was like then.

Birthdays are bittersweet.

You eat the cake, even if it's slightly hardened;
You aren't as excited, but your inner child is still celebrating;
You still make wishes, because there's still a part of you that believes in them;
You feel like everything is possible, and that overwhelms you with hope and terror;
You take a selfie of you smiling, knowing you'll feel like you both failed and succeeded when you look back at it.