I think the other two fetters, that define a Sotapanna, are no less significant than "seeing through ones own imagination of their self" -- i.e. they are:
- vicikicchā (doubt, uncertainty) 1
- sīlabbata-parāmāsa (attaching to ceremonies)
Maybe these are a superset of (more general than, thus greater than) the "overcoming sakkāya-diṭṭhi" attainment.
Also I think that sakkāya-diṭṭhi is more and less than "one's own imagination of their self" -- I think it's literally "true-body view", and its antonym is to not seeing (or view) the five aggregates as self -- which I think is an intellectual position or realisation and, moreover, an experience.
It's a preliminary attainment, see e g. How are 'conceit' and 'identity-view' not the same? (or here where I describe that as analogous to being an addict in recovery, still experiencing conceit and suffering and so on).
I gather that a further thing that's required of a Sotapanna is heedfulness, i.e. though they may have heard (and understood) what right view is, but it takes heedfulness to keep it in mind (see e.g. Jayarava's analysis of The last words of the Buddha for a description of appamādena).
Also I think the doctrine (of "four stages") meets the criteria defined in the handful of leaves, i.e.
And why have I taught these things? Because they are connected with the goal, relate to the rudiments of the holy life, and lead to disenchantment, to dispassion, to cessation, to calm, to direct knowledge, to self-awakening, to Unbinding. This is why I have taught them.
However, what practical use can one obtain from using the four stages?
Yes I think the suttas say more (or in more detail) about the right conditions for stream-entry than later stages (see also Can someone give references of the four stages of enlightenment in the four major Nikayas?).
I think the other stages (or other fetters) is a reminder of how much more (or further) the way to cessation is than only, merely, or even wholeheartedly adopting "right" view (intellectually) -- i.e. after that there's still overcoming any anger, sensuality, clinging, conceit, and so on -- see also e.g. What is effluent?
1 Looking for definitions of vicikicchā, I found vicikicchā and suttas that define it, which says (I summarise):
- AN 1.15 and 1.20 says doubt arises and increases with unwise attention (and, vice versa, decreases)
- DN 2, DN 25, and MN 39 suggest it means "uncertainty as to what things are wholesome"
- At MN 16, vicikiccha applies to Buddha, Dhamma (that includes any part of the teaching, the noble truths, the three characteristics etc. and also who speaks the truth or falsehood [SN 43.13 and AN 3.66]), Sangha, the training (sikkha).
- MN 23, it is compared to a fork
- SN 22.84, doubt is compared to a "forked road"
- SN 12.32, doubt is about whether one as abandoned the asavas, in other words whether one is an arahant or not
- SN 46.51, doubt is twofold: there is doubt about the internal and doubt about the external
- AN 7.54, doubt does not arise about undeclared things because of the cessation of views
I wondered about the definition in SN 12.32 -- if overcoming doubt is associated with being a sotappana, why is it still being mentioned in the context of deciding whether one is an arahant?
I think the answer to that is here, part of the definition of "conceit" ...
a Sotapanna can only give rise to true conceit, viz:
- thinking one is superior when one is superior
- thinking one is equal when one is equal
- thinking one is lesser when one is lesser
... i.e. a Sotapanna, when conceited, would see correctly that they are not an arahant.