I'm not a PM but I sympathize with how difficult it is to discern where a project is up to when it comes to software, especially when you can't come up with short enough milestones...
They see this and it fits a pattern and so they are fairly skeptical.
Those responses usually upset me, because I feel that my experiences are being devalued. I read the comments and I compare them to my life of the past five and half years and they just aren't the same. It can be hurtful to have casual snide remarks made when you know that the people you work with are kind, thoughtful, intelligent, hard-working humans through and through.
But I also know that other people have had bad experiences and what they hear sounds like other things they've heard from shitty managers and colleagues, so they're cynical. If I talk down to them then I am devaluing their experiences. So I try not to, even though my personal nature is to be an arrogant wanker.
Context switches are annoying to the engineer and costly for development. Each context switch probably costs between at least 15 to 30 minutes, maybe more depending on what the engineer is working on. If that happens 4-6 times a day, you've potentially burned 1/4-1/3 of the day. I spent close to 3 hours in 3 unrelated meetings. So, 1/2 of my day was spent task switching and not really giving 100% attention in the meetings because of the constant task switches. Frustrating and don't feel like I made any progress today, on my first day back on an overdue week long vacation.