One thing that works well for me is going working-to-working. Get a simple, de-scoped, incomplete, probably crappy version done end-to-end. Now it's not about finishing, it's about improving. And if it was worth building in the first place, it will beg for improvement. And then it's easier to just keep turning the crank, working-to-working.
In Pragmatic Programmer, this is called the "tracer bullet" approach. Basically just another word for end-to-end, but with the emphasis that by completing a slice end-to-end you'll get feedback much faster (as in the feedback tracer bullets provide when shooting a target).
Hmm, how about... End-to-end: "can really implement?". Tracer-bullet: "can adjust aim?". MVP: "can make user happy?". Though there's more to each.
So then market fit exploration benefits from tracer-bullet, but you might do iterative reimplementation instead. And it might be overkill for a one-shot market test. MVP is largely orthogonal to end-to-end - "Submit button emails founder who does the thing by hand over breakfast" is fine MVP but isn't very end-to-end. And a non-MVP non-product end-to-end can be tracer-bullet or not. A soundly architected low-debt end-to-end yes, a hackathon high-debut "to adjust, rewrite", or a throwaway end-to-end exploratory spike, no.
