Variables are things that can change over time.
The number of words on this page is a variable. My level of motivation as I write this page is a variable. My computer is not a variable. Whether my computer is switched on or off is not a variable (they are discrete states.) The amount of electric consumed by my computer is a variable and would include the two states mentioned and everything in between.
The two states create "either/or" thinking whereas the variable notation creates possibilities and begs the question "what makes this vary" and " what does its variation affect"?
Please see Variables for more examples.
There are many ways to identify variables in a system. - A Question - Documents - Stories - Preliminary Diagrams - Behavior Over Time Graphs - Critical Loop - Brainstorming Variables - System Needs
See Create a List of Variables for a final word of advice.
Remember: Practice makes perfect. Start identifying the variables (the things that are changing) around you, in what you see, in what you read, in what you hear.
The "Rolls Royce" way of ensuring we have identified all the variables is to build out a complete CLD with a large number of participants. This can result in a huge model taking many weeks to build....
The next stage is Filter Variables.