Is there a word for lowering the importance of something by summarizing it?

Often times someone will tell a long winded story, and then someone will reply with something like "So basically you just had a bad day."

Another, I think better example is when someone will talk a lot about existentialism, and then someone else will reply with "So basically 'to be or not to be, that is the question.'"

Or another example, someone will talk about Cuban-American relations after the cold war, and someone will reply with "So basically America plugged their ears and pretended Cuba didn't exist."

I don't think the word 'oversimplify' is good enough, because it can actually increase the importance of something. For example "So basically if you don't recycle, everyone will die of global warming."

Solution 1:

Trivializing or trivialization doesn't explicitly describe the act, but it describes the effect you're talking about.

This is in conjunction with WS2's answer: you reduce (or maybe minimize, as per Centaurus) the story to the point where it is trivial.

Solution 2:

What you are talking about here is reduction, as expressed in reductionism or reductionist.

Reduction is a perfectly valid process, not only in mathematics - reducing a mathematical argument to its simplest form - but in things such as philosophy etc.

But the examples you give are of things, which I would assert are perversely reductionist.

The Oxford Dictionary Online does note that it is often DEROGATORY. Hence it may be possible to leave out the perversely, above, and sufficient to say the arguments are reductionist.

Solution 3:

The rhetorical device known as bathos is defined as

an abrupt transition in style from the exalted to the commonplace, producing a ludicrous effect.

[Wikipedia]