The only single (albeit two-sided) factor that has ever mattered: what do I (or the team already know), with the flip side being, what does the customer want?

The only single (albeit two-sided) factor that has ever mattered: what do I (or the team already know), with the flip side being, what does the customer want? I like boring technology - stuff that Just Works™, is well-known, and is going to be [relatively] easy to maintain/update Everything else is just icing