What problems do you struggle most as an engineer in a leading role (CTO, tech lead, manager)?

Becoming some kind of engineering lead or manager has its own set of new skills to master and problems to overcome. Suddenly you aren't a single contributor anymore. You are responsible for other people and the work of several peoples.

• What are the main challenges and problems you face?
• What are some hard lessons you learned?
• Which skills and competencies do you work on improving?
• What are your resources to improve and learn those skill sets?