YOUR RESOURCES ARE LIMITED. You only have so much time and money to do your work, including the time and money needed to keep your knowledge, skills, and tools up to date. You can only work so hard, so fast, so smart, and so long. Your tools are only so powerful. Your target machines are only so powerful. So you have to respect the limits of your resources.
How to respect those limits? Know yourself, know your people, know your budgets, and know your stuff. Especially, as a software engineer, know the space and time complexity of your data structures and algorithms, and the architecture and performance characteristics of your systems. Your job is to create an optimal marriage of software and systems.