In 30+ years of programming, vast majority of bugs I've fixed were diagnosed with a few strategically placed print statements.
"I just print values. When I’m developing a program I do tremendous amount of printing. And by the time I take out, or comment out the prints it really is pretty solid. I rarely have to go back." — Ken Thompson in the book Coders at Work by Peter Seibel
It works a lot of the time (but not always, not great for debugging locks on stdout, for example). If you only have time to learn one debugging technique, this is the one to learn.
In 30+ years of programming, vast majority of bugs I've fixed were diagnosed with a few strategically placed print statements.
"I just print values. When I’m developing a program I do tremendous amount of printing. And by the time I take out, or comment out the prints it really is pretty solid. I rarely have to go back." — Ken Thompson in the book Coders at Work by Peter Seibel