Tom's Fourth Law: With Power Comes Complexity

Software that does something very simple is usually (usually) very simple to develop. Software that does something complex is usually very difficult to develop, and therefore usually very difficult to use, at least for its first few generations.

(As an aside, this actually applies to computer systems in general and in fact most things in life, not just software development. Food for thought.)

"Well, duh!", I'm sure you're saying. This seems intuitively obvious. But you would be well served to keep this in mind when:

• designing software - building something powerful is probably not going to be simple. Don't skimp on the design.
  
• building software - building something powerful is probably not going to be simple. Don't fool yourself into thinking it'll be easy.
  
• managing a software development project - building something powerful is probably not going to be simple. Don't expect things to move quickly or proceed without problems.
  
• selling software - using something powerful is probably not going to be simple. Set your customers' expectations accordingly, or your tech support department will suffer.
  
• buying software - using something powerful is probably not going to be simple. Set your expectations accordingly. Alternatively, ensure that your vendor has a very good tech support department.

Conversely, if you WANT your software to be easy to use, keep the functionality simple. Focus on the few essential pieces and build them well. (For good examples, check out just about anything built by Google.) Just don't expect to have all the same functionality at the end of the day.

You probably don't need most of it anyway.