KISS Principle

Keep It Simple, Stupid (KISS) is a design principle oted by the US Navy in 1960. The aformentioned principle states that most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design, and unnecessary complexity should be avoided. The phrase has been associated with aircraft engineer Kelly Johnson. The term became popular in the 1970s

An example of KISS in a funny format

In Software Development the KISS Principle contains these key points:

A simple system doesn't have too many parts and, more importantly, doesn't have too many dependent, interconnected parts.
A clear mental model of an application is a good sign of its simplicity.
If you ca, try to reduce the complexity of the features your managers try to build, by proposing an equivalent solution. You will need good, business related arguments.
Delete every bit of code which are useless for your present needs. No one knows what will happen in the future.
Avoid global states and behaviours like you would avoid the plague.
Don't create too many layers in your application.
Abstractions are useful sometimes. Sometimes means; not all the time.
Polymorphism and use of the interface construct can be useful as well, but don't overuse them.
Make clear where the dependencies of your application are managed and be careful not to couple classes if you can find a better solution.
Don't try to show your knowledge when you're coding. Keep in mind that anybody should be able to modify it easily. Even somebody with no expertise.

Why is it good?

It helps you to be more deterministic in your programming

Any Disadvantages?

THe KISS Principle is not always the best thing to do, as you think too simply and forget about the other crucial but sometimes additionally considered add-ons to put in your design which could put it over the edge over other competitors.

Sources: (click on them to see them)