Quick Definition: An explicit statement of your intent regarding the relationship you wish to develop with the girl.
An SOI can be delivered very early on during a pickup, or revealed later during stages of comfort in order for the girl to know the PUA’s intentions. An SOI is useful because it eliminates the possibility of the girl doing a LJBF routine, and also shows her that you are interested, which is a good reward if she is also interested in you. SOIs are useful for direct game, as well as changing the tonality of a conversation as it stalls.
An SOI can also be bad, as it removes the element of suspense and guessing regarding the PUA’s intentions. SOIs can be used with double meaning to balance the negatives via calibration. For example, an SOI such as “I really feel a strong connection you, (read her reaction, then calibrate) you’re so much like my little sister” lets the girl know you feel connected and may be interested in her, but she is unsure if the sister connection means you could also want to be friends with her.
The calibration can work equally if her reaction is a positive one (i.e. DDBL), and the PUA follows “I really feel a strong connection to you” with a calibration. “I am trying so hard not to kiss you right now.”
Source: Charisma Arts