Runtime errors in competitive programming generally stem from issues like division by zero, out-of-bounds access, or illegal memory manipulation. Commonly overlooked elements include array indices, especially in nested loops or dynamic resizing operations. Division by zero can also happen unintentionally, especially when dividing by a variable that might be zero in some cases. In languages that handle memory allocation manually, invalid memory access or pointer issues often cause runtime errors. Testing with values that could lead to such exceptions, such as zero or negative numbers, and double-checking conditions and constraints can help mitigate runtime errors, making code more reliable in competitions.