Beginners can fall victim to self deception if they are not careful. I've seen it a few times now. Some new player has a good game and automatically chalks it all up to skill, regardless of how much luck was involved. Let's face it, luck is always involved. But we're only human, and we want to feel good about ourselves, and we want to be in control of our own fate. Unless we lose, then it's just dumb luck.
Poker players like to brag after a win too, I'm guilty of it. The more you try to convince other people of how good you are, you convince yourself. The problem here is that the next time you sit down to play, you are over confident and reckless. You may not pay attention to tells or see things that aren't there. You may rush to decisions, after all, why think it out? "I already know what to do, I'm awesome at this game!"
Hopefully this all doesn't apply to you, but it is good for us all to be aware.
Another factor affecting novice players is that they treat their winnings as profit. One would buy-in to a $20 game and cash out at $50. They might braggingly say (and therefore think) that they made $50. But they didn't. They made $30. Similarly, they easily forget their losses.
As players mature they eventually figure this out or go broke. The best way I know to maintain self-honestly is be keeping records of everything. You should make an Excel sheet recording every win and loss with dollar amounts and time spent playing. You could also use software like Poker Tracker or an on-line tracker like pokercharts.com. I know it is tempting to not record that tournament you signed-up for and only lasted 2 minutes because your first hand was those pocket rockets that got busted. It's a bad beat. It hurts your stats. But you would have recorded it if it was the other way around.
Don't cheat at the tables and don't cheat yourself. You'll become a better player for it.