One of my favorite sayings is, "Man plans, God laughs".
Bill Lemon over at Cleantech Finance Insider has an interesting post about why investors are looking for 'the plan' from a venture leader.
This is an illuminating post for those who want a job at a startup.
First, note that the founders of any given venture are under significant performance pressure from the investors. Second, business plans are important for the investors, and the team working to realize the vision. Third, investors are as interested in how a given venture is a home-run opportunities as they are how the venture can be salvaged when things go awry.
Know that when you join a start-up, you're going to be asked to do a lot of stuff that you wouldn't at a much larger company w/clearly defined roles & specialization. You may end up working on something that is far afield from the vision you were brought in to solve. And, if it's important for the investors and the founders to know how to salvage an investment, you better have one for yourself as well.
So, focus on the success of the venture, focus on making the plan happen, focus on helping the founders in any way you can. But, have plan B & C tucked away somewhere so you can pull them out when the time comes.