I don't consider it to be a hunch, being psychic, or anything of that nature. It is a different way of observing (not just seeing, but taking in details) and processing information, often small cues. Cops tend to develop this more than most people because it is a literally a matter of life and death. Even now, when I see something that doesn't make sense to me, I try to keep my distance and figure out why it doesn't make sense. Usually it is pretty quickly figured out, often indistinguishable from the actual perception.
If I do not perceive an innocent explanation for the activity, I act accordingly - usually by moving away from the problem if I can. If someone stops at a stop sign as they should, then sits there for more than a second or two with no one coming, there are few likely causes. They will vary by time of day.
If it is after about 1600, and certainly by 2000, there is a good chance that they are impaired - at least 30% will be; some times of the day and days of the week, it's over 50%. If they have license plates or a dealer plate frame from out of the area, they simply may not know what they need to do. In this college town, that's not as valid as a predictor as it might be elsewhere. Most of the time, it is simply someone who is indecisive. Just saw a great example of that in a pursuit video today, as some soup sandwich sat like a lump as a cop tried to get past their lawfully stopped car to continue the pursuit. Idjit simply would not get out of the way. I've seen that a staggering number of times, both while driving a squad car to a call, or while on foot at the call. The number of people who are completely unobservant and can't make a decision with the necessary alacrity is truly sad. Then we have the simply stupid. I work in a building that has one public entrance. It has double doors and good signage, and is clearly designed to be welcoming. Every other door that faces a public area has "Staff entrance only" in letters about 6" high, right about eye level. The number of HUA persons who pull on the door handle (repeatedly!), then try to peer through the dark glass, is staggering. My office faces that door, and I am hard to see, but I can see them. This happens 3-5 times a day, and some will actually try more doors that are labelled that way. I don't think I have seen anyone I would suspect to be malicious - which leaves "dumb as a bag of hammers" as the cause.