Overthinking leads to over-enginnering, because humans aren't great at knowing what to do with all the free time we'd have if we did our job in 10% of the time :) Perhaps overthinking is required to keep us busy. Even though we all claim our time is money, in reality most get paid by the hour and not by the amount of work that has been accomplished. Plus complexity gives more weight to what we do, allowing us to claim that there's no shortcut to where we're going. That degree, that level of experience, are all job requirements that protect us.
Experienced entrepreneurs often fall for this trap. Too much prior knowledge of a particular industry leads them to quickly find faults in most ideas, and the just-do-it attitude that leads to simple approaches that stun everyone slowly fades.