im not committing on the things i can't handle.why would i?you'll just face humiliation in the end so why commit? But if so happens your in tight situation like this, better ask for someones help, or schedule it on another day, perhaps another weeks, learn to say no but explain the issue.
I guess every one must have gone through times when he is overcommitted. The last year I had at college was really intensive, lots of projects should have been accomplished and to be submitted on its due time, I was always behind my schedule, fortunately I still could meet the the deadlines. :)
Don't commit to avoid overcommitment. Why you want to commit on first hand if you can't execute on time? If you commit to please others than can you please them with undone commitments?
Overcommitment is more contagious to relationships and professional life than anything else. Not making commitment and working to make it done is more pleasing and surprising attitude for others than overcommitment.
Overcommitment leads us towards distrust and lack of trust is the basics to failiure.