I think it is understanding the algorithm that does it. I also recommend that people learn how to read a regex by writing a small recursive program to match sp

I think it is understanding the algorithm that does it. I also recommend that people learn how to read a regex by writing a small recursive program to match specific regexes. After you look at a regex and think about how it might work, intuition follows. Actually writing the bit that turns the regex expression into said program isn't as important though. Doing that by hand 5 times is enough IMO.