When is enough enough?
That's a hard question and the answer always depends on our situation and risk tolerance. Especially if we are trying to build something and we cannot predict how the market will evolve by the time we (eventually) complete it. We often can't see the end from the start, which is in itself discouraging enough. So we often don't know to what extent we should dive in a new and unproven idea.
Bigger investments in our products don't guarantee their success and we can't be sure that they will delight people so much that they will be ready to spend their hard-earned money on them. There are many examples of failed projects despite their (at first seemingly) sufficient funding. Two of the more recent stories I discovered were about the Kickstarter project Brydge, where a budget of $800000 didn't work as expected and about two brothers, who were both programmers and invested around $200000 of their own money making a variety of apps (8 to be exact), just to find out a couple of years later that they have only made a bit over $4600 from them. The last story was also very touching, but unfortunately I lost the link to it.
These aren't isolated cases and they prove that spending must be very well grounded. Otherwise it has the potential to destroy our lives before we even know it. This is true for all makers no matter the industry. The "I have nothing to lose" mentality isn't entirely correct, because as long as we live, our life will be threatened by every decision we make. It will be also irresponsible to others if we don't care for ourselves, since this increases the chance that we'll feel in a position to help them too. (What is most often forgotten today is that we carry a collective burden.) If what we do has started to affect others negatively, before it even affects us, then enough is probably enough. Stubbornness can sometimes be a gift, but if we persist doing the wrong things, it can have a rather disastrous consequences. We must be able to find out when the returns of our additional effort are no longer positive, thus we need a higher degree of awareness of our own possibilities (knowledge of ourselves), the context in which we apply them (knowledge of the specific domain), and the blue ocean we try to develop (deep understanding of the innovative idea backed by tight collaboration with our customer).
The MVP often won't be very viable, simply because it will face other me-too products that are equally well funded. This makes creativity, speed of innovation and speed of getting feedback very important in the initial phase of product development. Even if we find that our product has its first roots in the marketplace, our resource reserves might have been depleted, which won't allow us to continue. Even if we're profitable, we might have lost our energy completely, which won't allow us to continue. Even if our product is successful, but we took credit and stakeholders now want their money back, effectively telling us that we ran out of time, we won't be able to continue. To ensure we preserve our breath, we must also pay attention to our resource burn rate (valid for cash, time, energy) and adjust our decisions accordingly, so that the probability that our effort will become sunk cost is minimal. Every cost must be bound to a particular return that is larger or equal to it to be justified. No company can afford to do everything and the sooner we understand it, the better. What we will decide to do or avoid is at the end a very personal decision.