Where most blogs fail: Long lifespan

Sadly, the end of a lot of small to medium sized blogs is the same: left dead.

The problems or circumstances for what this happens can be varied:

• Loss of enthusiasm: As with everything new, at first there is a peak of hype in which we only think about ‘our blog', ‘what to post about', etcetera. But when that peak lowers, you have to start thinking about spending time as if it were a small job.
• Goal-oriented blog: Some blogs don't appear to share knowledge. Some blogs have ‘hidden' goals, like looking cool for a job we want (at a company we know takes into account having a blog). Those blogs end usually dead when the goal is achieved (or left for impossible).
• Loss of the original focus of the blog: A few blogs suddenly change the topics they talk about to something very different, lose their readers and end dead. IMHO it is better to open another blog for the new topics instead of switching too radically. Same applies with the language, I've left reading two blogs because they switched from english to german.
• No time for blogging: Blogging takes time, specially if you plan to do it on a regular basis. Thinking small code examples, building diagrams, searching for images, writing the text... You might have personal or professional changes that take out the free time you had before. For example I use Windows Live Writer to write down ideas or post drafts, so if I'm inspired one day, I can write down all the ideas before they fade out, and then write the full posts whenever I have time.
• Too much corporate blogging: The biggest example is MSDN blogs. Some of their blogs have awesome posts, but other blogs are dead since months or even years. Again, having a blog requires time, so you must be willing to write on it, instead of doing so just for work.
• Zombie blogs: This is my personal denomination for those blogs who have a low and prolonged inconsistent posting rate. Blogs that for example Google Reader suggests as ‘most obscure' (probably dead) but that, from time to time (usually a few months) post something. Only people well known and with a solid user base can relax so much without losing their readers.

As a small conclusion, blogging is for fun and sharing what we know, but you need to spend time on it.