What it is: Shift Left is a philosophy of software development, in which features are continually tested and vetted as they are created. Moreover, these tests are carried out by integrated teams, rather than separate product testing teams, allowing for tighter feedback. This is different from more traditional development workflows, in which testing takes place less frequently, and teams are less integrated.
What it does: Shift Left allows developers to catch software defects earlier in the development cycle and provides feedback that can aid in the design process. In a sense, Shift Left moves developers closer to the consumer experience of software, by exposing them to issues in the product as early as possible.
Why it matters: Software defects are much more costly and harder to fix later in the process, particularly after the software is released. Additionally, incorporating tester and consumer feedback at early stages can make for more effective products. Thus, though left-shifted testing might seem onerous, it can save huge amounts of time and money down the line.
What to do about it: Review your software development processes against shift-left principles. Examine whether testing— for defects, usability or other criteria—is being incorporated effectively in development processes. Make sure teams are integrated and share knowledge so tests are comprehensive and relevant, and such that test results and feedback can be fed back efficiently.