What Weakens Your Skills?
Just curious what weakens your skills because I literally have no problem with anything in my German tree, I practice every day outside of duolingo, and some of my skills are like in the red zone lol... Does this hurt me in any way, like prevent me form leveling up, or is it just a visual thing to say like "HEY YOU MAY HAVE FORGOTTEN THIS SO USE DUOLINGO MORE" ??
Lack of use (the time between when you learned it and now, if the words haven't been used in other lessons). Also, skills with lots of lessons decay faster, and may take multiple strengthens to get the skill back to gold.
So, basically, it is a visual reminder (as you have said) that you may need to revise the skill. And, as some of us don't like our skills any colour but gold, we revisit that skill and either do a strengthen, or re-do any lessons which have words in them that we cannot remember.