In my experience, most successful people (and by extension, people who run successful companies) don't really know why they were successful and often attribute it to their own actions (eg, I write great code), rather than luck or networking or having solid code reviewers or some external factor. Because of this, when they are successful, they often double down on whatever it is that they think they did the first time, and that frequently doesn't work a second time.
Maybe the first idea hit a niche that wasn't being satisfied by the market, and the second attempt tried to break into a heavily saturated market. Maybe they just lucked out by being in the right place at the right time, or having the right connection that could bring in a multi-million dollar contract, or...
From a broader perspective, I would say that the biggest and most common mistake that people make (engineers too!) is not to spend time examining the hows and whys of the success that you've had so far. Were you successful because you had brilliant ideas, or was it because you had a mediocre idea that filled an underserved niche market? Were you successful because you used Postgres or Ruby or Kafka or Elasticsearch? Were you successful because you created a culture of innovation and learning and team players? Or were you successful because you happened upon a fantastic solution for the specific problem at hand but can't generalize it to larger problems?
If you don't know why you were successful in the first place, it's hard to continue to be successful.
TL;DR: lack of introspection and evaluation of success criteria over time
Maybe the first idea hit a niche that wasn't being satisfied by the market, and the second attempt tried to break into a heavily saturated market. Maybe they just lucked out by being in the right place at the right time, or having the right connection that could bring in a multi-million dollar contract, or...
From a broader perspective, I would say that the biggest and most common mistake that people make (engineers too!) is not to spend time examining the hows and whys of the success that you've had so far. Were you successful because you had brilliant ideas, or was it because you had a mediocre idea that filled an underserved niche market? Were you successful because you used Postgres or Ruby or Kafka or Elasticsearch? Were you successful because you created a culture of innovation and learning and team players? Or were you successful because you happened upon a fantastic solution for the specific problem at hand but can't generalize it to larger problems?
If you don't know why you were successful in the first place, it's hard to continue to be successful.
TL;DR: lack of introspection and evaluation of success criteria over time