Newbie Question on Market

I've been browsing houses for a few months now and I decided to get serious recently. A house popped up that was in a good area of Pittsburgh, even if it wasn't the best house I still liked where it was at. Showed it to my wife and 2 days of research on the area decided to tour it.

I tried to set up a tour the same day but because of scheduling issues, we weren't able to get in until the next day, today.

When I woke up this morning I had an alert on my phone from Zillow that the house was now marked as under contract. Contacting my realtor she said that the other agent accepted an offer but would be willing to let me come anyway and put in a backup offer if interested. Literally set up our tour and then accepted another offer hours later.

The house has been on the market for less than a week in the Pittsburgh area. Is there anything I should take away from that? Is the market so hot that I need to jump on anything that looks decent on day 1?

Is this how house shopping goes? My realtor told me to not expect to get an offer accepted right away but the first time I'm interested in a property that turned out to not be the case. You just get shafted without warning? Like, wouldn't you want to wait a minute and see what other offers come in on your property? Do people tend to sit on offers