Very, very true. However, there are writerly workarounds that do not always require starting over from scratch. (There are times when nothing but ripping the manuscript to shreds will work, but if you can save the effort you've already put in, why not?)
To start with: nobody but the writer knows how the story goes. Changes to the story, before even an editor sees it, are invisible to the future reader. So look it over with that in mind.
Ex: 1 You need the character to be on the road for only two days between A and B (doesn't matter what mode of transportation--take your pick) but reality says A and B are only one (or more than two) apart. If this is your world, with your distances...your real problem is that you made the map before the story. It's a rubber map--change it. If that means changing eight previous chapters (or conflicting with the previous book set in the same universe, or it's the real world and there are real maps)...then you have to change this bit here. If you need the journey to take longer, throw a monkey-wrench in it. Person sprains an ankle, the horse goes lame, the car has a flat tire, weather delays the flight. If you need it to take less time, delay departure until it takes the time it should. (You're creative--you can figure out a way around this.)
The story must make sense to the reader, but the reader doesn't have to know what tricks you pulled to get there.
Ex. 2. Let's say it's important, for symbolic reasons, that A meets B at the vernal equinox, and you have imagined (because of where you live) that it's spring and the fruit trees are blooming...but the story location is somewhere on earth where it's still snowing or long past the blossom time of fruit trees. You have several options. Change the location to fit the symbolic elements you want to combine (if you have to send A or B or both on a trip to accomplish this...you can do that), or change one of the elements (it's not fruit trees in flower, but something else, or you change from flower-to-fruit as a symbol to another balance-element.) Changes to the deeper stuff in your story (symbolism, for instance) may open new windows in your own creativity and make the story even better. The first idea was the easy one; the next may be richer.
Ex. 3. Let's say you need a prop (a recognizable dagger for a murderer to use, a certain poison, a style of hat) that isn't available in the city/time/whatever where your story is set. You don't find out until you're deep in the story, which depends on this prop, that it cannot be where you need it when you need it, the way you thought it would be. Sometimes this blows the story (an airplane capable of flying the Channel in 1900 in a story that's not alternate history or time-travel or fantasy) but sometimes you can contrive a believable way to get your prop there--or substitute another reasonable prop. Selling that poison has been outlawed? Your would-be poisoner finds some in the back cupboard of a school chemistry lab, long forgotten. He/she is in the lab for a reasonable reason (best friend teaches chemistry--is concerned about safety of the students--asks our would-be poisoner to help clean out the cupboards--our poisoner pockets that jar.) That style of hat wasn't available in your city until X, but was available in Y? Your character (or someone who brings it as a gift) visits Y.
Be sure to connect changes to the underlying story dynamics--the motivation of characters. Let the motivations for the changes actions resonate through the story...this may require some backwards revision, but it will ensure that the changes don't stick out.
What you can't do is assume nobody else will spot the blunder, if you decide to ignore the research and leave your blunder in the story. Someone will, and someone will crow about it in the most annoying and hurtful way, implying that you're ignorant and stupid as well as incompetent as a writer. You're going to make mistakes--we all do, honest ones that result from not having access to every research source at once and a lifetime to check them all--but any source you have found, someone else knows about. Find a workaround of some kind--make it flow with the rest. Or, at worst, stomp around snarling for awhile and then start over. Most of the time it won't come to that.
(And has it happened to me? Yes. And have I ever had to start over? Yes. Grump. But not often.)