I know you're honest. I am too. Some people aren't honest, and compulsive liars do exist because I've met a few. I'm honest with my company, managers, family and friends, but there's one person I'm often not honest with. Myself.
I once heard Andy Stanley say we are the best sales people at selling ourselves on bad ideas. We make excuses and rationalize to make ourselves believe, "It won't hurt just this once." Then one time turns into many. This can be as small as sneaking a dessert or as big as breaking someone's trust.
When we sell ourselves on bad ideas, we're just allowing that bad thing to take hold in our lives so it's easier to repeat over and over until it's out of control. I'll share an example from my life. I'm a bit of a health nut and often experience this dishonesty with myself in regards to food. "Oh, that extra dessert is ok. I don't want to waste good food!" Before I know it I've lost track of my usual discipline and have to make up for it in the gym. Afterwards I think, "It would have been much easier to have not eaten those sweets in the first place, then have to sweat it out later to clean up the mess."
That's one thing to manage honesty when it comes to food, but what if we were dishonest with ourselves in regards to something much weightier? What if the bad decision is something bigger that blows out of control as in the case of Bernie Madoff? I'm sure he didn't start out thinking his Ponzi scheme would blow up into global scandal that it was and still is. He probably said to himself, "Oh I'll do this for a little while until things look up, and then I'll make things right." Then he started to get away with it. One thing led to another, and before you know it, tons of people had been swindled out of their life's savings. Those people's lives changed dramatically in an instant for the worse. It was the exact opposite of winning the lottery.
So how do you know if you're being honest with yourself or not? Stop when you're considering a decision and see if you have that little nagging on your inside. Is there a tension there that is asking for you to pay attention? Listen to the tension, and it will guide you in the right direction.
Continue being the good, honest person I know you are, and be honest with yourself too because you can!