Im talking purely kata and some basic techniques like punching, kicking blocking etc. I havent really thought about it before.

Good question.....

When I did Yang-Style Tai-Chi regularly back home, I found once I'd learnt the basic 24-forms, it was fairly easy to replicate them at home (Think "moving meditation" if that helps! )
However, Karate was and still is a different matter for me, I suppose without guidance its too easy to slip into sloppy kata and poor technique.

What he said.
We need that extra push that you get in a dojo, too. That push that takes you past the "I'm tired, so I'll rest now".