Can you actually motivate someone else? Think about it.
Can someone else motivate you?
Actually, no. The only person that can motivate you is you, and the only person that can motivate your team is the individual members themselves. Motivation is an internal result of what matters to an individual. It is the juxtaposition of those internal concerns with external stimuli that encourage or discourage action by each of us. If we see that certain actions on our part will lead to ends that we desire, we are motivated to take those actions. The key is that the actions must map to something that concerns us.
It's clear, then, that as leaders we cannot simply "motivate" someone by telling them why we think that they should do something. Rather, it is our task to understand them as human beings well enough to make our communication effective. Furthermore, the best leaders are those who understand their team members so well that they actually consider whether or not the team members' motivations are inclined towards any of the activities necessary to complete a project. Then, they adjust team assignments to keep those motivations aligned with necessary activities. If there are those not clearly motivated by the projects, it is the role of the leader to determine how best to engage them or, possibly, re-assign or otherwise find valuable activities for the team members that resonate with their own motivations.
This is the key! Spend some time with this idea. Consider all of the team failures that you've seen. Consider the fear-filled teams you've seen (or, God forbid, joined) and consider the source of the fear and the demotivation resulting from it. Where did it originate? Simply put, it starts in the lazy "motivation" efforts of a leader. Often using one of the basic fears that plague human beings, a weak leader will attempt to rule by force. Such an approach is never successful for long, and often will cause teams to spin out of control in one way or another.
As a leader, please understand that your team members are human beings. They are motivated by their emotional desires and responses in life. Help them to move towards those things that attract them and away from those things that repel, and you can be a very successful leader. Be a lazy leader and try to "motivate" your team members and you will not find lasting success--and will also very likely be miserable.