• At coding time? Depends. Higher level expertise required
• At compile time? No
• At link time? No
• At debugging time? No
• At unit testing time? No
• At run time on low loads? Rarely (Only if you are lucky / unlucky??)
• At lower levels of parallelisms like single core single processor systems? Rarely
• At higher loads and higher parallelisms? YES

As you can see concurrency problems hit you at the most inconvenient time. After the application has been launched and starts getting load, is that these problems hit you.
As professor Edward Lee said: “I conjecture that most multi-threaded general-purpose applications are, in fact, so full of concurrency bugs that as multi-core architectures become commonplace, these bugs will begin to show up as system failures. This scenario is bleak for computer vendors: their next generation of machines will become widely known as the ones on which many programs crash”.
Today we are witnessing this every day. The previous generation of programs fail repeatedly on newer multi-core processors. Most problems are related to concurrency and appear on higher loads. Rewriting these programs is a daunting task that most vendors are hesitant to undertake.