As a startup, your speed of execution is a function of your simplicity. It's about your only advantage over the big players.
Adding employees, adding products, and adding new markets increase your complexity non-linearly. ie. Going to 1 product to 2 products doesn't increase complexity by 2x, it increases it by 4x.
Avoid this complexity if you can: it makes you slow, makes you hire middle management, and makes what could/should be simple decisions, multi-dimensional.
So the lesson: stay as simple as you can for as long as you can. If you can't stay simple, don't underestimate the exponential drag of complexity.
Hope that's helpful