The secret is to learn what you need to know when you need to know it. I recently had to use some new js framework hotness; spend a couple days reading blogs, tutorials, and the docs, learn what you need to be productive and move on. Then dump it all, and jack in the next big thing for the next project. Rinse repeat.

No one knows it all, no one expects you too. You are expected to learn, get up to speed, semi independently and with little direction. It gets easier after you've done it a few times, then it get really old.