Should I feel obligated to work extra hours because of project mismanagement?

Agreed 100%. In my experience, barring servers falling over, everything can wait until tomorrow (or Monday). If you send me an email at 5:15pm, then you can reasonably expect a response tomorrow morning before noon. If you give me a task on Friday afternoon, you can reasonably expect me to begin it on Monday morning. If you set an unreasonable deadline, that's not my problem. (And if you make it my problem, this is no longer particularly a place I want to work.)

Now, to be fair to employers, it occasionally makes more sense to do something on a weekend or late at night, such as a deploy that involves downtime or some other critical factor, but it should not be required. As a manager in these kinds of scenarios, I ask for volunteers or I do it myself. I've never actually had to do it myself. Someone always volunteers to keep me company.

But the point is that it's not required. If your boss tells you to work late, or your coworkers shame you into working late or weekends, run the other way.

If you enjoy working long hours and giving up your weekends, knock yourself out. But don't do it just because someone else can't manage a project. (And, of course, if you decide to push back on this, do so respectfully, firmly, logically, and with full confidence that your time is valuable -- especially time with family and friends.)

Great response.

I am from Italy and I really care about productivity. What I realized is that rarely more hours results in better work.

The thing is: If you care about quality, then being too much pressured or fast-paced might lower quality. If you care about quantity... then why the hell are you paying a so-skilled person to do "quantity"-work.

Now...a small question. After I began reading HN and some startup info, I got the impression that, in many fast paced startups, this might be a "common issue", is there someone who could confirm this or I'm just making this up by myself?

I want to understand if the startup world (almost non-existent in italy compared to the rest of the world) consider the human behaviour a big part of the game or not. Right now I find that few startups or companies publicy share how they handle this situations and what they do to avoid this streaks.