One example I've seen first-hand and suffered is confirmation bias. Beginning programmers, at least, when they run into a bug, do not try to disconfirm what they think the bug is, but instead try to confirm it. For example, they'll put print statements for a troublesome variable after the line they suspect is causing the bug rather than before it, to verify that it wasn't bogus before hand, or better yet, both before and after the suspect line.