Three decades of working on enterprise systems comes with a ton of lessons, especially around performance. During my talk we go on a brief journey into some of the painful lessons learned designing and building high load systems that need to scale to handle 10s of thousands of concurrent uses running at many thousands of transactions per second. We will cover many of the obvious and some not so obvious impactions of high load systems, delving into some key design and development principals as well as important production support aspects. At the end we will briefly look at some examples of analysing scalability problems using Application Performance Monitoring. If you're interested in delivering highly performance systems, then this talk is for you.