Some people have mentioned communication and I guess a very important subcategory is negotiation skills. I feel most devs are bad negotiators especially when th

Some people have mentioned communication and I guess a very important subcategory is negotiation skills. I feel most devs are bad negotiators especially when thinking about hourly rates and the like. And (in my view) earning a good income is very important, so you can retire early for example. Or perhaps work less hours (might be difficult in the US, but in The Netherlands a lot of people work 4 days a week, for example).