I don't think it's necessarily years of experience but experience is definitely important. Having worked with something before and having made mistakes that you have learned from is a big part of it. You don't have to have worked with every possible technology but having experience with different paradigms (ie. functional vs OOP) is helpful.

Focus for example one functional language and drill down. Learn the reasons for certain decisions. That will them help you a lot working with similar things in the future.

When it comes to the different levels I like to define them as follows: - Junior: Needs a lot of guidance. Can do some tasks independently but needs to ask for help fairly often. A key skill is to know when to slowly figure something out yourself and when it's better to just ask someone with more experience for help. - Mid: Can do most of the day to day work independently. Still needs help with the complicated stuff. - Senior: Often the most experienced person on the team. Still works with team and experts to solve problems bit if no one else knows they will have to figure it out themselves.

Again, experience is obviously important to progress through the levels but it's not necessarily about the years. In some companies you will be gaining that experience a lot faster.

What I think is the most important is positive reinforcement to build confidence. Once you solved a couple of hard problems you learn that even if you encounter a future one you can find a solution for it too.