Sunk Cost Fallacy. Integral to human nature regardless of discipline.

And yes, the temptation to go 'But I can make *this* work!' is big, isn't it?

I think the real difference here between the senior and the junior programmer is that the senior programmer is so steeped in the craft that the subconscious can continue to churn until the senior programmer -has- the epiphany. The junior programmer never has that moment, so never sees any way but the hill they've already chosen to die on.