Many non-Japanese conflate sashimi and sushi; the two dishes are actually distinct and separate. Sushi refers to any dish made with vinegared rice, and while raw fish is one traditional sushi ingredient, many sushi dishes contain seafood that has been cooked, while others have no seafood at all.
It's the moisture and contaminents that break down the DOT 3 and 4 fluids which is the reason to change the fluid in the first place. If you don't change it, what happens is moisture enters the system via the vented fill caps on the brake master cylinder. This moisture along with dust, mixes and travels in the system eventually making it's way to the lowest points in the system.
The end result is this: When you step on the brakes, the pedal will go all the way to the floor but it will not stop the car. Brake fluid leaks are not something to worry about later. The safety of you and whoever else rides in your car is at stake. Next, I'll show you what are the brake fluid leak symptoms.