Explore advanced techniques for estimating system performance using first principles in this 41-minute conference talk from SREcon19 Europe/Middle East/Africa. Learn how to combine base rates to quickly answer challenging questions during system design discussions, pull requests, and technical reviews. Discover methods for estimating critical aspects such as regional failover times, proxy overhead, and system optimization potential. Gain practical skills to evaluate expected system performance without the need for initial implementation. Through examples and methodologies presented by Simon Eskildsen from Shopify, develop the ability to make rapid, informed decisions about system capabilities and limitations. Enhance your problem-solving toolkit with techniques like napkin math, inverted indexes, and decision trees. By the end of this talk, acquire the confidence to provide quick, accurate performance estimates in various technical scenarios.