Risky Business
We are each responsible for our own decisions, even if the decision-making process has been undermined by stress or peer pressure. The real test of character is whether we can learn from our mistake, by understanding why we acted as we did, and then exploring ways to avoid similar problems in the future.
Making ethical decisions is a critical part of avoiding future problems. We must learn to recognize risks, because if we can't see the risks we're taking, we can't make responsible choices. To identify risks, we need to know the rules and be aware of the facts. For example, one who doesn't know the rules about plagiarism may accidentally use words or ideas without giving proper credit, or one who fails to keep careful research notes may unintentionally fail to quote and cite sources as required. But the fact that such a violation is "unintentional" does not excuse the misconduct. Ignorance is not a defense.
"But Everybody Does It"
Most people who get in trouble do know the rules and facts, but manage to fool themselves about the risks they're taking by using excuses: "Everyone else does it," "I'm not hurting anyone," or "I really need this grade." Excuses can get very elaborate: "I know I'm looking at another's exam, even though I'm supposed to keep my eyes on my own paper, but that's not cheating because I'm just checking my answers, not copying." We must be honest about our actions, and avoid excuses. If we fool ourselves into believing we're not doing anything wrong, we can't see the real choice we're making--and that leads to bad decisions.
To avoid fooling yourself, watch out for excuses and try this test: Ask how you would feel if your actions were public, and anyone could be watching over your shoulder. Would you feel proud or ashamed of your actions? If you'd rather hide your actions, that's a good indication that you're taking a risk and rationalizing it to yourself.