Read the passage and answer the question that follows.
The New Year is a time for resolutions. Mentally at least, most of us could compile formidable lists of do's and dont's. The same old favourites recur year in and year out with monotonous regularity. Past experience has taught us that certain accomplishments are beyond attainment. If we remain inveterate smokers, it is only because we have so often experienced to frustration that results from failure. Most of us fail in our efforts at self-improvement because our schemes are too ambitious and we never have time to carry them out. We also make the fundamental error of announcing our resolutions to everybody so that we look even more foolish when we slip back into our old bad ways.
The author says that most of us fail in our attempts at self-improvement because _______.