In short you can't. You are going to seek out external agents that don't have direct day to day input/work on the product. This could friends or mentors. It's

In short you can't. You are going to seek out external agents that don't have direct day to day input/work on the product. This could friends or mentors. It's good to have these throughout your life. They basically ,on top of their friendship, offer a detached perspective which will give you the objective rationality you seek. May The Force Be With You!