And I can't speak for whether something is sustainable for a particular developer or not (everyone's situation is unique and needs vary quite a bit from person to person), but 8 months really isn't a sufficient time to gather enough momentum to make it in pretty much any business. It's said that people overestimate how successful their business will be in the first one or two years, and then they underestimate how successful it will be in years three through five. Momentum can reward entrepreneurs when they offer something people want, but they must have enough patience to weather the storms that inevitably come. There are many factors to make a business successful, but one of the biggest is persistence. Without that, you've already closed shop.