It’s well known in the non-mobile world that you shouldn’t rely on one market. However, in mobile, this issue seems to be more pertinent due to the hold some players have in the mobile market.
In terms of mobile, a single market might be, for example, selling to one customer, one OEM, one network operator or even via one application store.
I have seen many developers stung this way. For example, developers who once made a good commission on Handango now complain that successive commission changes have made selling software less viable. I have also known a case when an ISV was complaining that it took months to get their application on a well known handset OEM’s application portal and they were losing money as a result. A more recent example is the iPhone store where $1 applications have killed the gold rush and stifled innovation for the majority of developers. I have also seen a few examples where (especially small) mobile companies have become reliant on a single large customer only for this customer to change their strategy and drop their product.
The key problem is a market can change. The trap is that when you are successful, it’s easy to ignore the fact that things can change. You are bringing in money and you are happy. You ignore the risk that you are relying on one customer.
The solution to this issue is not to become complacent. This is especially so when you are successful. Find alternative markets. Develop alternative products in parallel. Also, don’t sign exclusives.