READ THIS FIRST.
How true is it? How true is it that we sin when we forget God? I have been learning lately what the things that take me away, or make me forget, God are in my life and have been limiting my association with them. (For me it is watching TV, Spending time on Facebook, Reading books that aren't Christian literature.) I have found that when I stop doing whatever it is that takes me away from Him, I think "Oh... God, I forgot You are here..." And when I hear those words it breaks my heart.
Watching TV, going on the Internet, and reading isn't sinning, but it does make me forget my Maker. Of course I want to stay away from sin because it is not in God's will for me, but I don't just want to stop there. I want to live a life that is PLEASING to my King in everything I do. Is it pleasing when I spend more time on the Internet, catching up with all of my friends and hearing all the latest news, than "meditating on the glorious splendor of His majesty"? Is He well pleased when I start obsessing over what is going to happen to so-and-so on this or that show next week? Does it please my God when I ignore Him? The answer to all of these questions is "no".
When we forget God, is when we sin. I can testify that this is truth because, when I do not keep every thought captive and meditate on the Lord, thoughts of temptation come. When I do these activities, they make me forget my King and put me in a position that leads to sin.
My desire is to please God. Not forget Him and shame Him.
"Trust in the LORD, and do good; dwell in the land, and feed on His faithfulness. Delight yourself also in the LORD, and He shall give you the desires of your heart. Commit your way to the LORD, trust also in Him, and He shall bring it to pass. He shall bring forth your righteousness as the light, and your justice as the noonday." (Psalm 37:3-6)