This is true in all of our lives. But there are some steps we can take when this happens.
1) Present the task to God. Ask Him for His guidance. Maybe He has someone else in mind that He wants to do a particular task. Ask Him if He want you to delegate the task, or if He wants you to do it.
2) Ask God to help you only make those promises that He wants you to keep. He will provide the time & the resources to complete those promises.
"It is better not to vow than to make a vow & not fulfill it."
Ecclesiastes 5:5 (NIV)
Use this verse to minister to yourself. Making a vow to the Lord helps us to stay focused on what's important -- fellowship with Him. It reminds us that He's vowed to give us, comfort, courage & strength. It keeps us thinking about His love & grace everyday. A vow to the Lord helps us stay faithful to our commitments. Through this verse, the Holy Spirit gently & lovingly reminds us of our vows & provides the inner power to achieve completion. I know that when i have kept promises, my spirit is at peace. When i haven't, i've been stressed that i need to get this done.
One thing that stands out in my mind is praying for someone. Don't say you will pray for someone if you're not going to do it. The Bible teaches us that prayer is not to be like a grocery list. But, it's definitely ok to make a prayer list. Sometimes we have to write things down so that we don't forget them. On Facebook, i am in contact with hundreds of people; friends, vendor friend, game friends, etc. And when i see someone ask for prayers or feel they need prayers, i will stop right then & there & pray for them. I don't want to run the risk of forgetting & breaking that vow. The same way, if i'm face to face with someone in the same situation. God may lay it on your heart to pray for them. Ask that person right then & there if you can pray for them & do it.
It's very easy for us to say we'll do something & then forget it. But as Christians, it's important for us to be and example & remember, God keeps all of His promises. Use Ecclesiastes 5:5 to minister not only to yourself, but to others through your example.