The think (here) Blog

Anyone who tells you to "under promise, over deliver" is lazy, afraid of failure, and values perception over reality.  Is a perception of hard work more important to you than actual hard work? Are you really that scared of failing?  Why on earth is "playing it safe" so widely accepted? 

When you look at it as simple math equations it is easy to see "Over Promise/ Then Deliver" has an overall greater impact when it comes to actual output:

The "Under Promise/ Over Deliver":
Under Promise -1 (from baseline output), Over Deliver +1 so -1+1=O Hooray for Mediocrity!

 "Over Promise/ Then Deliver":
Over Promise +1 (from baseline output), Then Deliver +0 so +1+0=1

Trivial though the values on the graphs may be, there is no denying the result. You can see by the charts above that even if you don't fully deliver, you still create (at the very least) the same output as the "under promise", but most likely wind up somewhere ahead of "expected output"(0).

If you think the under promise/ over deliver is better, you are still missing the point.  It does not matter how busy you "look" or how much you "over deliver".  What is important is what you accomplish.  What is the actual output?  I think by over promising you set the bar higher, you aim higher, and your net output will be much greater because you pushed yourself further. 

If you are more concerend about how a boss, C-Level, or client will percieve your output than actual input you have bigger problems than you think, and you have some serious prioritizing to do.