I find it funny that most hole-in-the-wall stores that have a door with a handle and a sign that says "Push" also have 1,000 other signs and posters and other information that I will not see as I walk in. If there was just one big, obvious sign that said "Push" and no other distractions, I might push on the door to walk through. But I will always pull the handle otherwise. Then one of the store employees comes to open the door for me and says "You have to push on it," and I feel stupid.
Resulting lessons include:
1. Real-world objects, images, and conventions trump any amount of text warning users of exceptions to rules, unconventional behaviors, and other gotcha's and pitfalls.
2. Every bit of text is a distraction from something, or itself will be overlooked. Less is more. Words and phrases > complete sentences.
Take your car, for instance. Does your panel read:
You are travelling at approximately 57 miles per hour. The current engine temperature is approximately 120 degrees Fahrenheit. Your lights are on. ....Obviously, this would cause problems.
I hope most people know this already. This post is for those who do not. Please, for the love of your fellow humans, make extra effort to make things easy to use, removing the need for long text to read through. Usually, this will save both you and your users time, and keep your users from feeling embarrassed because they don't know how to open a door.