Meaning of 上 as Result Complement
from the high position looking down

When the verb denotes upward action or direction, and the object denotes 'comparatively high position', '上' means 'up to (successfully)'

Example:

登山顶 - reach the mountain top (登 shows you are attempting to reach the mountain top, but doesn't clearly indicate you have done so successfully)

登(上)山顶 - reach (up to) the mountain top (登上 indicates you not only attempted, but also successfully reached up to the mountain top)

爬河堤 - Climb the river embankment (爬 shows you are attempting to climb an embankment)

爬(上)河堤 - Climb (up to) the river embankment (爬上 indicates you not only attempted, but also successfully climbed up to the embankment)




presents the result of the action:

When the verb denotes 'applying',  '上' denotes 'onto successfully'

Example:

穿外衣 - wear jacket (the action 穿 must be applied to a body)

穿(上)外衣 - wear jacket onto (上 shows the verb 穿 is successfully applied onto a body)

寫四個字 - write four words (the action 寫 must be applied to a surface)

寫(上)四個字 - write four words onto (上 shows the verb 寫 is successfully applied on to a surface)




presents the beginning and continuation of the action:

when the verb implies it is an ongoing action

Example:

她爱草原 - she loves grassland (the action love is a continuous action. )

她爱上了草原 - she fell in love with grassland (上 show the beginning of the verb 爱, and the verb 爱 itself is a continuous action)



吃上饭 is not an example for 'verb that indicates successfully apply'. It is an example for 'verb that indicate successfully acquire'


吃饭 - eat meal

吃(上)饭 - (successfully) eat (acquired) meal