Avoiding the "sadness" after the Big Chop.
Your hair will not be as long as you think it will be
The amount of shrinkage you get while transitioning is very different from what you will experience after cutting off your relaxed ends.
The curl pattern you see might not be the same
With your relaxed ends weighing down your natural hair, your new growth's curl pattern will appear looser. However, sans the relaxed ends, you could probably have tighter curls. Be ready for this. This is why I am against hair typing while transitioning. This can be a big letdown for a lot of transitoners post big chop.
Your hair will require more maintenance
While transitioning, the amount of maintenance you have to do to your hair when it comes to moisturizing and daily upkeep is not as much as what you will be doing when fully natural. Natural hair requires moisture. You will have to step up your moisturizing game. While transitioning, your hair might be okay with just doing the LOC method, but after you big chop and your hair does not stay moisturized, don't be afraid to change your method. Try the LCO method instead.
Not everyone will love your hair, even you might not
After you big chop, you might not love your hair. It might feel like a stranger to you. You do have to be ready for this possibility. You have to learn to work with your hair to love it. Also, realize that it takes time to fall in love (for some people). If you find that you have "post Big Chop depression", it is okay for you to put your hair in a protective style for a while. Another thing is that maybe you love your hair and others don't. Remember...IT IS YOUR HAIR. You cannot please everyone.
Lastly, the decision to Big Chop and when to Big Chop is yours alone. No one can tell you when to do it. You will know when you are ready to Big Chop. For now, love your hair.. love yourself... and learn from your hair. For me, going fully natural goes beyond my hair, it is an empowerment.