Have you tried tracing your reasoning that leads to this feeling, step-by-step, and see which step bumps the odds to 5%? For a programmer, the analogy would be "the output of this code is 5%, which is suspiciously high, let's trace the program with a debugger and see which instruction is responsible". More often than not, you find that there is a path through your code that you haven't thought of before, or a step that seemed innocuous enough has a different effect from what you expected. Another standard technique is to work backwards from the final answer and see where it comes from.