Stop trying to motivate people
Stop trying to motivate other people: you can't! Instead put your efforts in to creating an environment around them so that they choose to motivate themselves.
If you are managing people think about the environment your staff are working within. Is it in itself motivating? As you walk in the office does it lift you up or get you down? We aren't talking décor here although that can play a big part. We are considering the environment you set to enable your staff to act.
Think about three specific abilities that you can embed so that your people can motivate themselves.
Ability to decide - how can you give your people the ability to make daily decisions for themselves? Look to give them more autonomy.
Ability to learn - how can you give your people the chance to learn daily? Are you allowing them to make mistakes and so learn?
Ability to act - how are you giving your people the ability to act on the decisions they make and the lessons they learn?
The more you can put in place the more likely they'll be motivated. If they constantly have to come to you for approval then they will become dependent on you and not act if you aren't there.
So think about what you will now do to create an environment where your people can do the three points above. If you don't manage people then think how you can use these if you have children, work with project teams, and even work with animals.