Since you are a developer and mental model, one out of 10. The Pareto principal formulated by the Italian economist Wilfedo Pareto, who realized that 20% of inputs into a system will give you 80% of results. As a developer, it means that 20% of the features you will work will give you 80% of the recognition. 20% of the bugs will take you 80% of the time to fix. 20% of companies will be worth working for.
The Pareto principal applies everywhere in your developer career. Your job is to identify it and focus more of your time and effort on the 20% that actually pays off.