Something is badly wrong. My program crashed, or printed nonsense, or seems to be running forever.
Beginners have a tendency to blame the compiler, the library, or anything other than their own code.
Experienced programmers would love to do the same, but they know that, realistically, most problems are their own fault. Fortunately, most bugs are simple and can be found with simple techniques. Examine the evidence in the erroneous output and try to infer how it could have been produced. Now you know something of what happened, and where. Pause to reflect.