You will not convince me you can complete "40hrs" of work in "10 hours," doofus.

That's just 10 hours of more effective work. The other 30 hours you're lying to me and cheating me out of what I'm paying you.

Of course, you can get away with it, because you're clever, there's way too much money in tech jobs sometimes, and people are trusting - and you deliver! Even if the work product is only meh; it's better than what those other chumps were doing, right?!

Until you get caught; until someone in the recruiting community in your field/stack/industry catches wind of this post or that post; or you slip up and double book stakeholder meetings; or your background check shows multiple employers; or ....

Hiring is guessing.