Can you overcondition hair?

Yes, you can. If your hair is too soft, then it will not hold a curl. So finer hair may need a conditioning shampoo and then skip the conditioning step all together. The shampoo should leave it detangled enough.

Also, we all know that too much protein will dry out the hair and make it prone to break.

Pictured is NuExpressions Humective moisturizing conditioner. It does a great job with coating the hair for thermal styling, but it seems to have a drying effect if left on for too long. After 20 minutes, it really needs to be rinsed out. Many conditioners that have protein boosts in them really do need less dryer time. It is best to follow the manufacturer's instructions on the jar.