When there are lots of ways to do something, choose simplicity. When you can make an existing "thing" simpler, choose so. If you ever aim for something less than simplicity, it's because you're experimenting with something, or it relates to self-improvement (which we may talk about another time). In most other cases, simplicity thrives.
Say, writing a story. A story consisting of difficult words, that in the eyes of the writer are mundane words, or perhaps slightly challenging but not too difficult for native speakers of that language, yet extremely difficult to the rest. A story aims to convey something, a message, an idea, something. If you write something and asks the reader to check the dictionary or access the translator every 3 words, or even every sentences, it's inaccessible. The reader finds it hard to read, annoying to switch between a dictionary/translator and the content, if they expect the story to be easy, fun, and relaxing to read. Therefore, choose simplicity.
It's not always the case though. You may want to add some difficult words to challenge the readers. If things come too easily, they might find it bored. Occasional hard requirements challenges the reader to think instead of to absorb, to act instead of to react, to be active instead of to be passive. Without boredom, your reader wants more!
Say, programming. Programming isn't just about the code you write; it's also the programming language that you choose to write. A lively programming language like Python and Ruby serves easier understanding, for yourself, for your readers, and for your future self (when you look back at your own code). An ugly programming language however, doesn't motivate your readers reading them. Even if they need it, they force themselves into it, and come out sad. It's difficult to write in an ugly language and expect beautiful code. Yes, it could get beautiful; for the programmer must be really expressive and understand how to make it easily understandable despite the ugly code! Don't expect an average person to write a beautiful code in an ugly language. A beautiful language however, unless abused, easily produce beautiful code. Even so, it's up to the programmer to make it beautiful, readable, clean, and appreciate the spaces between codes. The best, someone whom can write beautiful code with beautiful language; something so easy even a layman (whom at least know that code executes in these manners) understand the flow.
Say, in life. If you chose to buy bread from one store, stay with it. When visiting another country, though, you might want to try out various stores' flavors; at your home town however, choosing something and stop thinking about it, fares better in the longer term. If you have to choose every single little thing every time, you'd be out of attention very quickly. By fixing the little things to simplicity, to your instinct, you could spend your limited attention somewhere more important, somewhere which worth more than the little things. Simplicity freed up your attention from making decisions every single time.
Perhaps the "life" example is easier to encounter; the other two on "writing" and "programming" doesn't, though. For you, readers, might not be familiar with programming, but at least familiar with writing, which you do in school, either long time ago, or still writing now (in or outside school). We shall skip the various ugliness that amateur programmers do and speak about writing.
Every single word matters. Do not waste words. It doesn't mean you can't use long sentences, though. If you use longer sentences, ensure that every phrase in that sentence is expressing something, not a waste. An example is "to be able to". Some articles one read previously uses this phrase. It's fine if it occurs only once or twice, but not more. Replace this:
"The phone needs a charger to be able to charge."
"The phone needs a charger to charge."
Simple, right? We cannot totally omit waste of words, unless you read what you write over and over again, give it to several editors to do the checking before publishing. We can, however, aims to reduce unnecessary words.
For further references, check "Omit Needless Words" of this book.
Simplicity is necessity. By including only necessary words, your end-product is more understandable to its readers. By dealing with only necessary stuffs in life, you live a simpler life. A simpler life is not a bored life, though; you just focus your attention on whatever matters! When you aim for easier understandability when others read your work (or other stuffs), you aim for simplicity indirectly. Let's keep it simple.
The Elements of Style