Some sites practically force / really encourage you to leave a review (e.g. spam you with email reminders until you do, have seriously annoying UI that won't go away until you review). Apps will constantly ask you to review it, but this can be circumvented by clicking the link and ignoring it.
But if a review can be tied back to your account (e.g. the review is not private, rather public) this could hurt you long term. A good example of this is airBnB. If you have written less than stellar reviews to some hosts, some superhosts (those that require initial contact, e.g. not the ones with lightning bolts) might potentially ignore you because you are a liability of poor reviews.
This ends up limiting the overall options you have with airBnB when you need to stay at a city. Not only that, some hosts would rather see you left a good review if you only used airBnB a few times.
Another example is writing an honest review about your employer, whether its on reddit, glassdoor etc, and that review happens to be bad. If these things end up being traced back to you publically, you might be burning bridges / not having recommendations down the road.
It is selfish that I write good reviews because it gives me less problems down the road, thereby making ratings not as honest for everyone else. At the same time it can be incredibly selfish writing a poor honest review, because not everyone rates things equally (what is average rating, is it 3 or 4 stars?). What if that was a first time airBnB host with no ratings (having a poor first review is like a death sentence)? What if your stay as poor and it wasn't entirely their fault (e.g. outside noise was bad, washer broke, your sleep was awful, cockroach infestation next door, etc).
My point is, sometimes you need to write a review, and its hard to define what an honest rating is, and how detrimental it can be to you and the other party, especially if its on a personal level. I prefer to leave the honest part on just the text portion of the review, not on the 3 out of 5 stars part.
Sometimes people just need a helping hand and a good review goes a long way even if the service was mediocre. As long as they showed good faith and did their best I give them a 5. I know how hard it is to run a business from personal experience, and I know what its like to be on the consumer getting shafted at the end. I try to be as fair as possible