#1. You'll spend most of your time cleaning
This is the truth that no one tells you. You need to constantly clean the apartment and this will eat up almost all your life. If you miss a few days, the filth can be so overwhelming that you will never start and live the rest of your life in squalor. Sorry.
#2. The rent is not fun
Every month, a big portion of your income goes to rent. It's sad and traumatic event that it doesn't get easier. Learn to think of your income as amount that remains after rent. It's the only sane way. And for the love of all that's holy, do not add up in your head how much rent you've paid since moving.
#3. You will get scared by random sounds
It's creepy to be alone in a space. Dunno why but it is inherently something about nobody having your back. Yeah, you can walk around naked ( see #4) and all that but weird sounds will freak you out. It's often that I think a spirit came visit me...or worse, pigeons! I also almost had a heart attack when my dryer decided to fall unexpectedly next to me into the night. Not recommended
#4. You will be naked. A lot
Ah, the benefit of being alone. You can just BE NAKED all the time. And everyone says this a an amazing feeling. Just walking Adam-like through your space is a fuck-you signt to the rest of the world. Ahh...but, truth? Not so much. It's actually impractical to be naked and uncomfortable and if you have neighbors with direct view in your house maybe not such a great idea. Yeah, you will do it in the first week than maybe never again. The hype is NOT real.
#5. Food doesn't cook itself
Who knew? Remember when you went to the fridge and found food whenever you wanted to back when you lived with your parents? Yeah, now you'll find mold if you didn't take care of this by you know..cooking and buying fresh products. Sorry.
Ah, one more weird thing?
The food you cook will never ever ever ever have the same taste as "home-cooked" meal. Is honestly baffling and sad.
Just a few things on the top of my head. I know they are all whining!! but that's the list about. There are many many advantages too and the serenity of being alone outweighs all of these. But there are some things :D