First time I made it to the portal in Deadmines, I asked a guy standing there what it was all about.
I wasn't using Alla or Thottbot back then and it was the 1st instance portal I had seen. He said "Well first you have to be in a group...".
Silly me, I didn't even try to enter it, went out and got a group. We made it to the Shredder Robot thingie and they told me we were done. I said "Where is Van Cleef?" and they all shrugged and hearthed out.
Fortunately I found a guild shortly after that. They told me Shredder was like the 1/3 point of the instance. They also told me that you DON'T have to be in a group to enter an instance, as long as you meet the other requirements.
Ahhh, youth!