One of the key lessons from business schools is this: ignore sunk cost. Forget about it.
Once you have made that expense in a business development effort, it’s down and irrecoverable. It’s in the past. And no future decision should be made on this basis. Turns out this rationality requires a lot of emotional labour from us as humans because it’s hard to not get emotional in decision making in moments like this and that’s in fact what separates failures from success. The point is, it’s one thing to take lessons from failure and it’s another to fail backward and use past failure and unrecovered investment as an excuse to hide.
They said Thomas Edison tried and failed 999 in his bid to create the light bulb until the 1000th time when he became successful and we can learn from his resilience.
For the fact that it hasn’t worked until now despite all you have invested in it does not mean it cannot work. If you have considered it worthwhile, stay on it.
Do not give up!