Singular Vs Plural......

Sometimes the usage of singulars and plurals in English fascinate me and what is more fascinating is how we use it in our everyday life. For example, the thread between "I" and "We" is so fine that sometimes I ponder as to what I should use. The alphabet "I" or the singular form, if used often, denotes self-centredness, ego, pride or bragging about oneself. But everyone does have to think about oneself and their priorities and if thats termed selfish then so be it. Again the word "We" or the plural form is again important cos at certain times individual interests have to be set aside and team work or others' interests become important. There again its our wish that we choose "we" over "I". Its just that a proper balance between "I" and "We" neds to be maintained. It is something like the relationships we have in entity-relationship diagrams like one-to-one, one-to-many, many-to-one, many-to-many. So similarly it would be I-to-I which would mean you set goals for urself and achieve them, I-to-We which would mean you do something whose output will help others or prove beneficial to them and so on.
English is an interesting language. It is generally observed that plurals are formed by appending a single alphabet 's' to the singular form of the word....but in practice transition from the singular to the plural is not easy for many. But there are certain words in English like sheep which remains the same in both singular and plural forms which is actually interesting. So that would mean no demarcation between usage of "we" and "I"....both are considered as one. I guess that would mean selfless love...in which two people would care for each other more than they care for themselves...feelin happy in other's happiness and feeling sad in other's sadness and accepting people as they are.
It just depends on how, when, with whom that we need to choose our "I"s and "We"s else the sentence would sound grammatically incorrect or inappropriate.