I made various things. Two examples to show the range - Enterprise grade business process middleware for Telcos. Software and microcontroller firmware for law enforcement. And then everything in between.
I have never really thoroughly analyzed why I am successful with the estimate and delivery. I think I'd be way more interested in it if I was late. Since I am not I do not really care. I just am and this is enough for me.
I am eternally grateful to my University (nothing to do with comp science btw) and teachers though who taught me not to blindly remember the rules but how create those. I guess this helped me to become who I am.