I used to play with Lego as a kid, largely the Space stuff and then Technic.
In the past few years I've picked up Lego again, with the realisation that during my absence Lego Technic had matured more than I, and that my adult income now allowed me to get all the big beautiful sets.
My MOC focus initially was Lego Technic, but I have now expanded into trains.
Lego, especially Technic is engineering.
I like the integrity behind the Lego Technic approach they officially quote as "Authenticity, Functionality and Challenging Build".
If it is done in 'reality' it can be replicated in Lego Technic. My personal maxim when starting a project is that 'it's possible'. The only question is the scale required to achieve the functionality. Smaller usually being better.
I don't claim to be as genius as some of the others I've seen here. But every little achievement brings some satisfaction.