Yes, and no. Theft can be a strong possibility, but not "all the time". It depends a lot on where you lock the bike, its value, and how you lock it.

I have had two bikes stolen twice in about 10 years. One was a hybrid worth about $1k. It was locked with a cable by the side of a Walmart in a neighborhood of questionable reputation. It took me about 15 minutes to get in and out and the cable was cut when I came back. The other was also a hybrid worth about $1k. It was stolen while locked with a cable, in the underground garage of my building. However I have another "cheap" bike from a big retail store locked with a very cheap cable lock in the same garage, and nobody stole it.

So now even if my contract says I can't bring a bike in the apartment, my "expensive" hybrid takes the elevator with me and stays in my living room. I also now use a thick U-lock because cables are risky. But even then I know very well that leaving it locked with a U-lock outside for any prolonged period of time is also risky.

If you have a "nicer" bike than average, you have to be mentally prepared to have it stolen at some point. Not "all the time", but maybe a few times in your life, depending on your luck and locations.