How good are you at taking responsibility for your actions? If you grew up being screamed at, belittled, or physically abused for even the smallest mistakes, maybe you learned that owning your actions was dangerous, to be avoided at all cost. You probably developed a lying habit (even when caught red-handed) or maybe you became a perfectionist to avoid any suggestion that you might be less than worthy. As an adult, you've had to learn that taking ownership of your decisions, as well as your mistakes, is part of being a grownup.
Wait. You have learned to accept the consequence of your choices without beating yourself up, right?
If you haven't worked through that stuff, your first instinct when confronted about something today might be to deny, and it's definitely not comfortable; it can take you right back to being a kid. It may seem simplistic, but I find it empowering to admit when I've screwed up; it's like I'm saying, "That's right; I made a mistake, and I'm sorry, but I'm not going to be bullied into a scary place over it. People make mistakes. I'll do better next time."
Living in the truth is just so much easier than trying to keep it covered up; at least that's my opinion.