The Singleton pattern promises a simple way to ensure one class instance with global access. However, developers warn it introduces hidden design problems. This approach creates global state, making systems harder to understand and modify. What appears convenient early often becomes technical debt later, complicating long-term maintenance.

Senior engineers frequently avoid Singleton due to serious drawbacks. It creates hidden dependencies, makes unit testing difficult, and causes state to leak between requests. Tight coupling between classes follows, reducing flexibility. Passing dependencies explicitly, while sometimes tedious, yields clearer code and easier testing, promoting better overall design.

The core issue is that Singleton obscures a system's true dependencies. Any part of the code can alter global state unpredictably. The alternative is straightforward: if passing a dependency feels annoying, that's a sign to improve the design, not to default to a global singleton. Better architecture always wins.