Happiness and expectations

If there is one thing that increases happiness (or makes life less miserable), it is having realistic expectations. This applies in many different ways. A few examples.

• Unpleasant things happen all the time, but they are much less unpleasant if you take for granted that they will occur (or if you see them as opportunities to sharpen your claws).
• People - including your own children, and certainly your partner - hardly ever change as much as you might want. You might be able to get them to change certain aspects of their behavior, and you can of course instill certain values in your children, but their character is theirs, and whatever you achieve will be within the limits of that character.
• Information is often imprecise or irrelevant and sometimes incorrect or completely wrong. Depending on the "size" of your question, you can spend anywhere between a few seconds to a whole lifetime in finding the answer.
• As a general rule, things (cars, computers, cameras, clothes, etc. etc.) last less than you would like. Having a realistic idea of how long they tend to last would diminish the irritation. 
• For many medical conditions - and especially somewhat vague problems like recurrent back pain or headaches - there are no quick fixes, and sometimes the solutions you finally find, after trying all kinds of different (traditional or alternative) options, are only partial. 
• Politicians have much less control over a country's economy than most people (including the politicians themselves) think;
• Last but not least: having a realistic idea of your own abilities and of how much time and effort it can take to achieve something can help avoid a lot of frustration.

Of course, this is just the beginning: the next step is quantitative information, e.g. how much unpleasantness to expect, how much change you can achieve, how long it will take to obtain certain information, etc. An example of this would be: a book with one good idea is a good investment, a book with two or three is a very good investment, and a book with even more good ideas is a great book.