Learn Portuguese (Portugal): Pois é, esta cadeira é muito desconfortável. - That's right, this chair is very uncomfortable.

The phrase pois é is a very common discourse marker in Portuguese used to strongly agree, confirm a shared thought, or say "That is right" or "Indeed". While sim simply answers a yes-or-no question, pois é shows you are on the same page as the person you are talking to, likely agreeing with a complaint they just made about the chair.

Why do we use é (from the verb ser) instead of está (from estar) to say the chair is uncomfortable?

We use é because being uncomfortable is treated as a permanent, built-in characteristic of this specific chair's design. You would use está for temporary states, but unless the chair is only temporarily uncomfortable, a badly designed chair is inherently uncomfortable, so it takes ser.

Why use esta cadeira instead of essa cadeira?

The word esta means "this" and is used for objects physically close to the speaker, such as the chair the speaker is currently sitting on. If the speaker were agreeing about a chair close to the listener instead, they would say essa cadeira (that chair).

Why doesn't the adjective desconfortável end in an "a" to match the feminine noun cadeira?