You're in Portland, so you're at 45.5 degrees north. You are able to see Polaris, the Pole Star, at 45.5 degrees above the horizon. As the Earth spins once a day, all the other stars will appear to rotate around it. Anything closer to the Pole than 45.5 degrees away will always be above the horizon and always visible. We call these circumpolar stars and constellations. They will get low down and close to the horizon but never dip below it.
Anything further away, however, will dip below the horizon at some time. So these stars will only be visible at certain times. And anything closer than 45.5 degrees away from the South Pole of the sky will never rise above the horizon at all. If you want to see those, plan a trip to Australia! (Which will demonstrate a few other things too - the Moon looks upside down from there, and its phases occur the "wrong way round". Figure that one out!)
All that changes at different times of year is which non-circumpolar stars we can see, because we're travelling around the Sun so as the year progresses, different parts of the sky are above the horizon at night. If we could turn the Sun off for a day, then you'd be able to see all possible stars you can ever see from Portland at some time during that 24 hours, though not all at the same time. All that changes is which of them you can see at night. And so there are constellations known as seasonal. For example, Orion, which is not circumpolar at your latitude and definitely a sign of winter. In summer, it's above the horizon during the day so you can't see it, but there are other constellations you can't see in winter.
I'm in London, England, about 52 degrees north, so there is a bit more that is circumpolar here. Polaris appears a little higher in the sky than it does in Portland. (That is, when you can see it at all - on our damp island, the view is so often blocked by clouds! Which is why we have no major telescopes. It would be a huge waste of money and so British astronomers tend to travel a lot to where the "seeing" is better. I had a friend at university whose personal tutor was an astronomer and he was so often away in Hawaii - nice work if you can get it!)
To go to the extreme, let's make an imaginary visit to the North Pole. Polaris will be directly overhead, and everything will be circumpolar. The sky view will be the same every night all year, and all that changes is what compass direction any star or constellation is in. We can't see any constellations on the south side of the equator of the sky, EVER.
For the other extreme, let's visit somewhere on the Equator. Polaris will be on the horizon, nothing is circumpolar, and then it would be true that the constellations you see are exactly the ones you couldn't see six months before. And over the course of a year, you would be able to see every constellation there is. That's the only place your statement would be true.