Why is it that people that can't program always seem to think they know how long it should take you?

Because they have no idea?

I have little to no knowledge when it comes to rocket engineering, hence have no idea how long it might take for anything.

To be fair, as developers we tend to never correct them. If a manager sets a deadline for 3 weeks away and no one says "no, we can't do that". Then they're going to go on assuming building similar products only takes ~3 weeks.

Of course, there's definitely plenty of managers that just don't care/pay attention. Or in my experience, they spent a few years as a programmer back in the 90's and think they're still one of us.

FYI: you're clueless about most things as well

Don't you know, they have surpassed mortality and receive the gift of clairvoyance.

@Jilano Oh, they are absolutely certain it couldn't possibly take as long as you say. If they really had no idea, I'd be perfectly comfortable with that.

I had someone ask me if "I was finally finished" after I taught myself a new language (SimSCRIPT), and developed a model in it, in 3 weeks. The company that invented the language said it would have taken them 2 months, minimum. Yet I was "slow".

@ModernShoe I don't pretend to know their business as well as they do :)

This isn't about customers not knowing how long something takes. This is about them being certain that it couldn't possibly take as long as it is.