This is literally the best ux pattern you can have. It is intuitive - user immediately discovers it when performing the obvious action, it increases the user experience (more text to read) without any real downside.

It is the first thing I suggest to anyone when I see someone didn't implement it.

I've never heard a complaint about it until now.

This is only true if you assume users always scroll down while reading and the only reason they scroll up is to find the header... but many of us scroll up and down while reading and find the re-appearance of the header to interfere with our goal of reading the content. So there is a clear downside for us "up and down" readers.

I don't know what portion of users we are though, I'm glad to see I'm not the only one!

I consider it context-dependent. If a site is intended for users to jump around to different pages often, then sticky headers make sense. If it’s designed for long-form articles or scrolling through feeds, then non-sticky headers make sense. When I have implemented them on my own sites, I try to keep them minimal and unobtrusive. But I also have never heard this complaint specifically, until now.

The user discovers it because it is practically forced on them. It is awful UI.

It might be useful if you wait until the user has scrolled more than 20% of the viewport and not pop it out immediately.

I absolutely hate it. If you haven't heard a complaint about it, you haven't tried hard enough to get feedback.

There is no context which makes it OK.

>>without any real downside

Wow, impressive blindness!

Seriously, have you ever used one? Because most people do not read monotonically downwards. We often scroll back to see something in a previous sentence referred to in the spot we are reading. So we want to go back one or two lines. Bot NOOOOooo, the header pops up, covers 1/4 of the screen, so now we have to scroll that much more, pushing off the screen the other text we hoped to keep on the screen, and it might even go through a few adjustments. So, now, what was a non-event less distracting than turning the page in a book or magazine has now become a fully distracting scroll-fest.

Is that clear enough for you?

>>This is literally the best ux pattern you can have.

NOT EVEN CLOSE. The best User Experience pattern is to give the reader what they asked for AND NOTHING MORE. Nothing more for you, nothing more for your advertisers, and nothing more for them. We click to read the content, LET US READ the content, ALL the content, and NOTHING BUT the content. We'll even understand if some proper STATIC adverts are placed in the content, and we might even click thru if you've shown us something relevant and interesting

But as soon as you start putting motion and other distraction in the adverts, my priority becomes NOT reading the advert, but figuring out how to get it out of my face. And if by some chance I remember it, it is filed among "companies to avoid".

Why does it seem everyone who deals with advertising, from the execs down to the programmers, so stupidly thinks only of the first-order effects — "Grab Their Attention!" — and not the second-order effects, where being so offensive — surprise! — offends people...

It's awful for the user. There is no reason why scrolling up should perform any other action then scrolling up the content. Zero benefit for anybody involved.

You could just have a "hide bar" button. Dunno how you get it back, maybe put your design smarts there.

Stop making things "intuitive" and expose explicit options to users.