The doctrine of self varies in what is assumed to be true and what is taken to be a self.
The notion of self is a massive cause of psychosis. In dependence on it one thinks; 'i was, am or will be..', 'i am good because of this..', 'i am bad..', 'this is mine, may this be mine', 'this is my self, my self is good, is bad or may it be otherwise' etc
This idea is a ground for a lot of decision making. Ie one delineates other people as not self and one's own thinking & body as a self. One then might think; 'i am bad because of this painful circumstance, may i be in a pleasant circumstance, may my self thus become good, i will attain a pleasant state by causing grief to 'not self'.
Here it is basis for greed, ill-will & delusion. If the idea of self turns out to be a false delineation, empty in meaning, without a referent which can be established as a truth, then the whole line of reasoning leading to thoughts of ill will to another would turn out to be a tought of ill will in general in that it would have to be reconsidered as a baseless strategy for attaining happiness.
If there is no self then how would one treat good the elements which can be grasped by wrong view to be a self when one cultivates the element of cruelty towards other external elements which are otherwise identical to thr internal ones a body is a body, life-force is life-force, intellect is intellect, feeling is feeling; in the worst case it will turn out as a practical impossibility and element of cruelty will affect that which is taken to be personal as well, thus one might be harming oneself by harming others whilst cultivating elements of ill will, cruelty & delusion based on an untrue doctrine of a self; dwelling in wrong resolve & false expectations.
Furthermore if one treats oneself good by treating others good, thinking; 'my self is made good by making others good, i will remain like this'
This might turn out false, if that which is taken to be a self turns out to be not permanent then it will change or cease, a further effort needs then to be exerted for maintenance of a good state. One remains enchanted by good states, it becomes the resolve. Resolve on existence, pleasant feelings on one end, unpleasant feelings on another, neither pleasant nor unpleasant feelings in the middle.
Therefore the idea of self also ultimately blocks the resolve on knowing the unknown though liberation by wisdom based on disechantment; as it maintains the perception of existence being worthwhile there is then a lack of development of the intellect due to frequent giving of wrong attention and the nourishment of hindrances.