Ask HN: How to know if you are an imposter

In my SW dev career I've met several smart and/or hardworking people but also quite a few on the other side of the spectrum.

The place where I work since almost a year, it seems that most people are either smarter, or working more diligently than me, or a combination.

Although nobody explicitly communicates that I would be performing sub-par, it makes me feel a bit uncomfortable.

My questions to the HN community:

- Is this feeling very common?

- How to know if this feeling is correct, ie I should bring my efforts to a higher level (you know, less wasting time, better focus, more diligence, work a bit longer). Or rather, it is just something I imagine, and probably a feeling a lot of people even more diligent have anyways?

- If it is just the imposter syndrome popping up, are there ways to tackle that, does anybody have overcome this?