How we change what others think, feel, believe and do
Desire happens when we want something. The strength of that desire can range from weak 'would like to sometime' to a raging thirst to possess something now.
The paradox of desire, however, is that once we have got what we desired, we no longer desire it and hence may no longer find it attractive in any way. People get trapped by this pattern, for example in the way they chase members of the opposite sex, only to dump them when they have captured their affections.
Note the difference between love and desire. I can love a person but not desire them. Desire is the need to possess. Arguably, true love is not about possessing at all.
Desire is the opposite of fear. Desire attract us towards something. Fear makes us want to run away.
Desire is triggered when we see or think about something we want.
Desire increase when what we want is visible, but just out of reach. It may also increase when we have closer contact with the item, but which we still do not possess. Supermarkets know this well, as they place foods and other items right under our noses.
Desire also increase with teasing, where we are offered something, and it is taken away, offered back, taken away. A variant of this is where the item is only available for a limited period. This is an example of the Scarcity Principle. This is seen in shops in the regular 'sales' they hold.
Desire is the opposite of fear, and as such is a far more useful emotion in persuasion. There are many ways of increasing desire, such as showing how it will result in the admiration of others or making it available for a limited period only.