> After working on too many projects in totally different domains, using different languages, how can one get rid of the feeling as if all these years' efforts are nothing more than illusion?

I've spent my career working in: supply chain, business operations, sales support, marketing, IT, data engineering, web analytics, business intelligence. And a few other bit parts like a stint at a healthcare consulting firm.

I fully get exactly what you're talking about, as virtually every job change involved a completely new functional area but also generally involved an entire industry change. Which involves a whole helluva lot of "starting over from scratch" while simultaneously dropping into more and more senior positions where a more typical hire would have a far more well-built foundation than I have.

> I feel as if the only thing I know is how to pick up any new stuff fast, but ultimately it's not gonna last.

The thing is, this is an incredibly valuable skill in and of itself. It's natural for you to be able to do this, but many people can't. Even if you forget the specifics of what you've picked up before, you

- Still retain the concepts and mental models you've developed previously, which causes you to look at things from a very unique/different perspective than those without that diversity of experience. That's infused in how you approach your work, even if you don't notice it. Think of it similarly to dogs - mutts are more robust from a lot of inherited disorders that purebreds suffer from[1].

- You have fewer sacred cows and domain biases. Depending on the situation, this can be a strength or a weakness. It's usually a weakness in highly regulated areas where those sacred cows and domain biases grew from a place of compliance and legal requirements, but a strength pretty much everywhere else.

- Your history is indicative of (successful) flexibility. This too can be a strength as much as a weakness. If a company/team/project is in a mature and stable place and wants to remain that way, you run the risk of getting written off as a job applicant due to your potential as a disruptive force to that stable-state or as a likely flight risk due to the lack of interest you'd likely have in doing the same thing for a long period of time. But for a manager/team with a diversity of needs or a likelihood of changing needs over time, you're seen as a perfect match and considered a valuable find.

The best advice I can give around imposter syndrome is just changing your perspective - you're a mutt, not a purebred. Lean into that as your strength, rather than dwelling on that as a weakness. Just like purebreds (i.e. someone who has only ever worked in a specific domain using a specific technology/language) will outshine you in some areas, you absolutely outshine purebreds in other areas.

Also have faith in whomever hired you. They were both aware of your history history when they hired you and knew the situation (and position) they were hiring you into, and determined out of all the candidates that you were the one they wanted.

My supply chain job came from a college job fair - I walked into the interview with the opening statement of "To be upfront, I know virtually nothing about supply chain, I just really wanted the neat swag bag you were giving away". Turns out they didn't care at all; they had one of the most sophisticated supply chain orgs in the world and were fully confident they had that expertise covered and could teach me whatever I needed to know; they were far more interested in a completely unrelated skill that none of their traditional applicants tended to have, which they were in desperate need for on a particular team. I learned after the fact that me getting this job caused a whole lot of drama within the college, because the supply chain program was so miffed that a non-supply chain student had "stolen" an apparently very coveted slot/offer that they place their students into while being completely ignorant to anything related to that domain.

[1] https://www.veterinarypracticenews.com/study-shows-mutts-gen...