"How do you think we come by our Spirit Guides? Are they assigned to us by some Higher Power as needed, do our primary guides choose us at birth, do we make agreements to work with them in this lifetime before our birth?" -- Sarah P.
Sacred Contracts
The popular perspective says that our guides are contracted prior to incarnation in this lifetime -- that they represent a team of entities assembled for a particular mission, of which you play the lead. Please note that I use the word "popular" to allude to a mainstream consensus among the mystics who discuss this idea; and the question from Sarah asks what I think...
The idea of sacred contracts and the decision to incarnate certainly doesn't originate with me -- I don't see how there could possibly be a definitive capital K-knowing, from anyone. Although choosing aspects of your life as a spiritual mission implies a consciousness prior to incarnating -- and although one could quickly hear this as an indication of multiple lives -- I don't personally think this has to be about reincarnation in the sense of on-going and continuous consecutive life-times.
I can only attest to what I contemplate. I can't even profess a "decided" opinion regarding re-incarnation or multiple life-times, but I do have a strong sense of awareness and memory about events just prior to this life. My "jury is still out" on reincarnation. Do you see the distinction? I also don't feel what we experience Before and After is necessarily even relevant to what we experience Here and Now.
Having prefaced this discussion with a big Question mark... I don't feel that your spirit guides are "assigned" without your input.
In keeping with the story-telling metaphor of film and stage, the full production of your story doesn't happen without supporting cast and crew. Although the roles various other people play in your life are spread out over our human perception of time -- they come in to play out certain scenes, to teach us through our collective dramas -- the characters may be cast in advance.
The word contract implies a bit too much inflexibility
I don’t feel that this script is set in stone -- unlike a book, your story is not linear and edited to the letter in advance before being experienced. Once you're "on location" new options may reveal themselves, and you (with the help of your guides) may decide a rewrite is called for, on the spot.
I think maybe games would be a better metaphor -- such as first-person virtual worlds. I feel that gamers are ahead of everyone in understanding how manifestation and reality actually function as filtered through the living human mind's experience.
The variables may be initiated prior to birth, but your free will determines the nature of the tangents -- the times and places at which a particular guide may be most helpful.
Some psychics talk about "exit points" -- predetermined points of evaluation that correspond with near-death experience.
A life, as a production, might also resemble the work-in-progress of situation comedies, serial story-telling -- full of potential improvisations and the magic that only happens in the moment. If your life could truly be read in a form that remotely resembles a book, the present would be wet ink, crawling into the page as you live it, writing itself in a wave, advancing and crashing on a shore of still-blank pages...
A more helpful metaphor might be the "choose your own adventure" stories, but on a sort of infinitely unfolding scale -- the choices you make in each moment of time determining the next potential set of options. This is why you can't really "get it wrong" -- life is a journey of spontaneous detours.