I learned that too-thick deep conditioner was breaking my strands.
I third this.
Deep conditioning is definitely good for my hair but I need something of medium-light density. Anything that's going to weigh on my hair doesn't get the green light anymore.
I was pleasantly surprised by Shea Moisture's deep conditioners. I bought them thinking I absolutely had to dilute them to death but I don't. They go on like lotion and rinse soft and clean.
Same thing with leave ins. My leave ins have to be almost water-like, even when I was natural. If I put a thick leave-in on my hair and tried to comb through... nope nope nope. No oils left in my hair or thick anything. Same with co-washing conditioners, which is why I'm now sticking with VO5.
Now I use protein regularly. It's an ingredient in my rinse out and deep conditioners, but it's very, very light protein. Keeps my hair strong and co-washing multiple times a week has proven really useful in keeping moisture.
Quitting shampoo late last year was the best thing I could have done and using lighter conditioners in general this year was the second best. I had a setback because I didn't do these things sooner but I'm on my way.