When other people estimate the size and difficulty of your job, they will tend to lowball it, because of the Dunning-Kruger effect: when they don't know what you do, they think they're practically an expert. You'll find them saying things like "it shouldn't take long for you", "it's not that big a job", "there's not much to it" or "it can't be that hard". You won't be able to convince them otherwise without teaching them how to do your job, because as long as they can hallucinate that they know better than you, they will assume they have a high level of expertise in your job, regardless of what it is.
Could you write a book? Yeah, of course, you just hit all the keys on the keyboard in the right order and there's your worldwide best-seller. You've got the idea for it already, and all you have to do is write it, which is just mechanical. Could you be a model? Uh, wear clothes and walk? I think I can manage that. Could you be a rock star? All you need is to learn an instrument then roll around in the piles of money, right? Pfft. Simple. Read the news? They tell you what to say!
You get the idea. Just try to remember, before you guess that someone else's job is pretty easy, that you know practically nothing about it, and that destroys your brain's ability to make that judgement.
Mokalus of Borg
PS - Estimating your own job tasks can be difficult for different reasons.
PPS - And that's a whole different issue.