Use the 80/20 rule, or Pareto Principle, to avoid overdesigning.
For conversation design, this rule is a way of saying that not all paths are created equal. 80% of users follow the most common 20% of possible paths in a dialog. Therefore, invest resources accordingly for the biggest impact.
Similarly, there are trade-offs in terms of perfection or completeness. It may take 80% of the work to really polish the last 20% of the project. In these cases, the unpolished effort may be "good enough."
Preventing errors from occurring is better than handling errors after they occur.