Considering this area of the forum is rather dead, I figure I may as well go ahead and do a post about the mentality of the 3 fixation.
Before I dive into it, a disclaimer of sorts: This'll be skewed towards 3w4, but I'm sure enough of it will ping the 3w2s. I'm a sp/sx 3w4 with 5, and 8 (while I don't think it necessary in typing/life, 5w6 and 8w9).
The 3 fixation isn't ever really dissected, and most resources will keep it rather surface level. It is rather difficult to dissect a type that wears so many faces, I'll do what I can to make it make sense.
First you must consider/realize that any type in the image triad believes that love is conditional, a commodity if you will. Each type structures their own reality to gain more of it. Due to the transactionary nature of this, I consider "heart" types as "image" types.
The 3 fixation is one that was born straddling the idea that they were born great, but inherently empty. Love/validation is the gasoline that keeps the engine running, and they weren't born with an alternative fuel source. In order to earn the most validation/love, one must be able to appeal to every person. Authenticity isn't really a concern (recall being born empty), because that doesn't earn the highest margin. Life is a game of love that a 3 seeks the highscore in. It allows the 3 to fuel their unending drive.
Goals are things that a 3 seeks to accomplish in their quest for love/validation, and for that, they have an unending drive. Not ever being truly present, they would rather look slightly ahead to control their impact (profit/loss), and net the most gain. I do not care for the idea that success is limited to any one area, it is simply an avenue for currency. With this motivation in mind, it is not at all hard to see why a 3 manipulates and wears different masks.
Action isn't a hard thing, it is simply something they do to accomplish a goal. The thing a 3 struggles with, is the idea of being emotional, or vulnerable. Those things don't have controlled impact, and usually stop/slow the progress to the goal. Often portrayed as shallow, they're simply unable to give emotion any credit in their quest for validation. In unhealthy levels, they will use faux emotion to manipulate an end, because they are ever focused on profit.
When actually pointing towards growth, a 3 realizes that life isn't very fun if everyone else sucks at the game. They slowly then start to realize that they can use their unending drive to assist others at being better. To truly put forth 100% effort and win. In very high levels of health, they begin to realize that emotions allow them a depth to the game they've never considered prior (think of 100%ing a game). Contrast this to unhealth when they let their inherent emptiness stop them from doing anything, because of the lack of anything.
I'm going to pause this here. I'd like to keep this thing open for discussion and a sort of thread I'll drop ideas in on occasion.