Conflicting Conclusions: When one diagnosis differs from another.

Oftentimes, patients find themselves hoping for alternative solutions to an ailment, or they go searching for a second opinion. In some cases, the conclusions are the same, highlighting one definite course of action. But in rarer cases, The second opinion seems to differ from the first! and the third from the former!

When there are differences in diagnoses and opinions amongst multiple doctors, what is the next step that needs to be taken?
How could doctors come together to form one optimal solution?
Can there be consensus when life by nature is complex?