Lifetime want
First introduced in The Sims 2: University, a Sim's Lifetime Want (or LTW) is a special Want, representing the Sim's ultimate goal, something that would make his or her life "complete".
A Sim's Lifetime Want is based on their aspiration. For example, a Sim with the Family aspiration will tend to have a family-related LTW, such as having a specific number of children or grandchildren, whereas a Sim with the Fortune aspiration will tend to want to earn a certain amount of money during his or her lifetime.
Lifetime Wants tend to be very difficult to complete during a Sim's natural lifetime, but when one is fulfilled, a Sim will usually receive a very large amount of aspiration and influence points, and their aspiration bar will be locked to its maximum, giving them Platinum mood for the rest of the Sim's life.
Once a Sim has fulfilled a Lifetime Want, they will receive another one, though fulfilling it is less important since a Sim will not lose their permanent Platinum mood.