Yes, it's the author plotting/Can't write a character to save her life (sung - badly - to the tune of Scotland the Brave)
We all like to see the hero triumph against impossible odds, which is part of the reason why we like underdog stories. We also like the hero to actually be moderately heroic - to do things rather than wait for fate or some kindly deity to drop it in his, her or its lap.
So how do we write that? Obviously there have to be obstacles, and they have to be real obstacles, things that could feasibly stop the hero cold or possibly even kill him. If there weren't any, the book would be dreadfully boring.
This is where a lot of authors come adrift and start to plot by dropping mountains. You've all seen it. Hero is going along heroing, things are starting to look good, then WHAM! and the mountain drops in the form of a catastrophic event coming out of nowhere. Some books get so bad about this that any time the poor hero starts to catch his breath the poor shell-shocked reader starts looking for the next mountain.
Pratchett punctures this beautifully in The Color of Magic in the sequence with the Gods playing games with Rincewind and Twoflower, causing random pieces of scenery to land on them and getting them (actually, mostly getting Rincewind) into terrible trouble.
So what's the alternative?
Characters have motivations. The hero wants to rescue an adoring maiden, cart off several wagon loads of gold, and settle down to a comfortable retirement with his adoring ex-maiden. The villain wants the hero to become a sticky smear on the ground. The maiden wants to be rescued. Everything outside whatever sends the hero off after this particular maiden should arise naturally out of the hero doing his thing, the villain doing his, and the maiden doing hers. If a mountain lands on the hero, it should land there because something the hero did pissed off someone else, who set up a large catapult and sent that mountain flying, or because the villain is trying to keep the hero out and launching pieces of landscape in order to protect himself and the maiden he's holding hostage. The reason the villain is holding the maiden hostage is another layer: perhaps her father owes him a lot of gold, or he's paying back an old grudge, or he's fallen for her and is trying to get her to marry him and this is the only method he knows.
For instance, in Sarah's Gentleman Takes a Chance Tom and Kyrie both want to protect themselves and the people of Goldport from a murderous shifter, without drawing attention to themselves because a guy who turns into a dragon and a woman who turns into a panther would probably not like the results of being known for what they are. Dante Dire wants to pin the deaths of thousands of shifter beetle larvae on someone, kill someone, and get out of the hick little town, and wouldn't object to doing so with an attractive companion like Kyrie. Rafiel wants to stop the killings and find himself a nice girl who can accept him for what he is. The killer wants dinner. The intersection of all these motives drives pretty much everything that happens in the book.
Your mission, should you choose to accept it, is to name the books that offer really good examples of the character's motivations and actions driving the plot, or if you're feeling contrary, the ones where the author is flinging scenery from on high. And explain why, of course.