When I wrote it, I had originally written "optimal" as "efficient", but "optimal" has multiple meanings here.
The point is, if you would arrive at a requirement of $x to implement the thing in an exercise where you decide to entertain all requests as a request for a legitimate bid, then don't quote an arbitrary figure of $y. Quoting $x works out the best for everyone in all possible cases, where the approach to quote an arbitrary figure falls down in more than one place.
What? Why am I a jerk for getting paid well? Or do you suggest that huge pile of money won't change my mind? If I still say no I think that means the quoting instructions were followed incorrectly.
> Quoting $x works out the best for everyone in all possible cases
Quoting $x is much more likely to result in resentment because it's the bare minimum to get me to agree. If I charge triple that or more I'm much less likely to be disappointed later.
And it's no big loss to me if I don't get paid to make this feature. That was my default state of being. So I aim high.
Hell if you give me 10 million USD to build a random feature on an open source project, I would subcontract to someone happy to do it for 9 million.
Charge upfront.