There are great answers here, but there's something you said, in both the title and body of your question, (well, in your original title, before editors removed it), that no-one here is speaking to:
the focus on "Change From Within", and "their understanding of suffering must come from within."
Here's why I'm putting a spotlight on the question:
1) Because everything is connected.
2) Because of the importance of the Sangha.
3) Because of the Buddhist focus on Anatman, rather than Atman.
4) Because of the value of "practices".
5) Because of personal experience, of impacts, limitations, and drawbacks--mixed blessings at best--related to this concept, that
... must come from within.
This emphasis on "change from within" is such a cultural assumption of the 60s, and of the New Age movement, and of Americanized Buddhism... but I'm not clear how much it was part of Buddhism's "original product". (Someone else speak to that?)
Does change come from within? Absolutely. Does change come ONLY from within? Absolutely not.
(Not dealing with, right now: whether enlightenment actually involves "change"... and is there anything that needs to "come from" anywhere.)
Following the numbering above: (1) ItsAllConnected: if the "inside" and the "outside" are actually One, then why not notice the intermingling, when doing "inner work"?
(2) The importance of the Sangha. A quote from Buddha: "Admirable friendship is actually the whole of the holy life. When a monk [or anyone else] has admirable people as friends... he can be expected to develop and pursue the Noble Eightfold Path." (http://www.viewonbuddhism.org/dharma-quotes-quotations-buddhist/sangha-monks-nuns.htm)
If change is from within, what does the Sangha do?
(3) Anatman, rather than Atman. This focus on what's "from within" can actually be isolating. I'm not making "retreat" wrong -- it definately has value -- but want to point out that we can be standing in the point of view of the "us" we're being connected with. Some of the most enjoyable meditation I've experienced stands in this point of view... and just standing there, and noticing how that interacts with feelings, can be transformative.
(4) Are practices "internal"? If it's all from within, then why sit? Because the internal and the external are in cooperation.
(5) When you stand in the point of view that "the real stuff comes from within", it automatically presents you with a quandary, whenever anyone tries to contribute to your process: you have to somehow make it "within", for your "self". And sure, approaches like that to "internalizing" things can be of real value...
but it can also add a "chronological step" (this has to happen, before that), that doesn't actually always have to be there.
We're in this together, and if what you're saying resonates / feels like a fit / aligns with the Four Immeasurables (equanimity, love, compassion, empathetic joy), then is that enough to simply run with it?
Or do I need to make sure it first "works for me"... whoever "me" is?
In a similar way, while it would be one form of separateness (superiority), for you to see your buddy as "needing you to tell him," it would be another form of separateness (isolation), for you to withhold because "he's got to get it on his own."
((Another thing I'm not going to try to handle right now: healthy "boundaries", which, lol, I think can paradoxically serve a purpose, even in a point of view of connectedness.))