Building a bad plot is like building a wall from children's building blocks. A slight nudge will cause the wall to collapse and the blocks to scatter. Building a good plot is like building a wall with Legos. Each plot block is linked together in multiple ways and even a swift kick might not make the Legos separate.
So, one of the things I do when building a plot is to look at each plot block and determine how many ways it connects to the plot blocks that precede it and how many ways it connects to the plot blocks that follow. The more connections, the better.