I have founded and wrecked startups, worked for them as an employee, helped them as a mentor. I play the role of the CTO.
I have worked as a CTO for 3 different startups. At two of them as was a co-founder (both got funded) at the third one I was an employee.
In all cases I was heavily involved with figuring out the MVP and I was the one who fought against the will to build a 'perfect' product that would cater for everyone.
My background for trying to keep things lean is rooter in my past, when I worked as a research engineer at Nokia, well before the lean startup idea came around. I love asking hard questions, testing the seemingly stable assumptions as well as figuring out 'tricks' for saving time with the product/software development.