Is Your Time Series "Forecastable"?

Picture this: You are working on a data science project that requires you to predict the demand of a product. Your manager or stakeholders tell you that if your model's forecasts are within 15% of the true demand, then we'll call this project a success. You can't wait to begin the project. You assemble the dataset, conduct data analysis, and notice that the demand of the product is very erratic with no obvious patterns. Nonetheless, you proceed by cleaning the data, filling in the missing values, and creating features that you think might be valuable for your machine learning model.