What skills do you actually need to retrain as an adult?

What do you mean by "retraining" - completely switching fields or diving deeper into a related area? The thing is, it's not really about skills, but about being able to admit you don't know something and calmly learn it from scratch! You need patience with yourself (adults tend to be hard on themselves for a slow start), the ability to find a good source of information instead of trying to learn "like back in school," and realistic expectations - it doesn't happen overnight. Honestly, the main thing is just to start and not give up in that first month when it feels like you don't understand anything.