To me, it is only a failure if the time you put into it can make you more money or fulfill you in a greater way if you put it elsewhere.
$100 may not be much, but if you are constantly churning out $100/month side projects and working very little to keep them up and running, that turns into big money fast.
On a side note, I must admit that at $19.99, I would not buy an app with the sole purpose of cleaning out my Twitter inbox -- maybe I'm not the target audience, but that seems like a lot of money for something that does a very specific task -- one that could be easily implemented by Twitter at a later time.
$100 may not be much, but if you are constantly churning out $100/month side projects and working very little to keep them up and running, that turns into big money fast.
On a side note, I must admit that at $19.99, I would not buy an app with the sole purpose of cleaning out my Twitter inbox -- maybe I'm not the target audience, but that seems like a lot of money for something that does a very specific task -- one that could be easily implemented by Twitter at a later time.