Welcome to the team! We all feel that way at some point. Others have given some excellent reasons why this happens... so I'll just leave you with a quote.
"If you're the smartest person in the room, you're in the wrong room." - Someone on The Internet
If it's research, it's normal. The beauty of HN is in it's diversity. You can't know everything, but we are all here to learn something, usefull or not.
Also, IT is an iterative process. Learn something and then something more. It all adds up ;)
Well that's a strange question. We learn all our life. Depending on subeject and it's level - you will find articles too complex for you even 30 years from now.
You won't face times when _any_ subject will be a kids' literature for you.
"If you're the smartest person in the room, you're in the wrong room." - Someone on The Internet