I see a lot of excuses in this thread and that's all they are - lame excuses.
If you know that you can't or may not meet a deadline then it's very simple - don't tell people you can. It matters not at all about 'design blocks' or problems or anything else as they should all be factored in at the beginning.
Too many lazy arse, greedy fuckers around with no clue about business is the biggest problem. As somebody else said though it can also be in part due to the price you pay...
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