WARNING: The following post contains plot spoilers for the movie Iron Man 2.
Never give your protagonist just one problem, goal, or obstacle to deal with at a time.
The only time to do so is in a short story, when you don't have space to develop more than one issue.
Otherwise, in a novel, if the hero faces one problem, solves the problem, and then faces another, in a neat chronology, the pacing drags. And your reader gets bored.
Remember: the ultimate goal is always to keep the reader engaged.
With that in mind, it's better to pile on the obstacles. If the hero solves one, there's at least two more still in the action queue.
Here's what I mean.
In the movie Iron Man 2, protagonist Tony Stark (played by Robert Downey, Jr.) starts the movie in serious trouble. The technology keeping him alive (that back story is in the first Iron Man movie) is also slowly poisoning him to death. He's always been a lone wolf figure, so he doesn't tell anybody what he's facing.
Meanwhile, the United States government targets him as a potential threat to national security and demands that he turn over his “Iron Man weapon.” Just when he's convinced them that no one else anywhere in the world has developed anything similar to the Iron Man suit, a technologically brilliant maniac turns up at a race track in a less-than-sophisticated (but no less deadly) version of Tony’s invention.
All of which happens in about the first twenty minutes of the movie.
And it gets worse from there. Tony turns over his company, Stark Industries, to his long-time assistant Pepper, and she shuts him out so she can sort out the company chaos. Because he's dying, Tony chooses to go out with a bang, and alienates his friends.
In other words, there’s never just one problem or obstacle to be faced at a time. Most of the problems are interconnected, which only increases the tension and pacing. Movie viewers stick around to find out how on earth Tony’s going to finagle his way out of the huge mess he’s in.
Readers of your novel should be motivated to stick with your novel to the very end to find out how your protagonist is going to solve all of his/her problems.
What two or three problems or obstacles is your protagonist facing in your novel? What can you do to increase those problems and raise the stakes even more? Are there ways you can interconnect the problems to make everything worse?