tad-desha-kaalau vidhivat pariikShya
yogasya maatraam api c'aabhyupaayam
bal'-aa-bale c' aatmani sampradhaarya
kaaryaH prayatno na tu tad-viruddhaH
Having given due consideration to the time and place
As well as to the extent and method
of one's formal practice,
One should, being constantly aware
of one's own strength and weakness,
Persist in an effort that is not inconsistent with them.
This is not a metaphor. The aim for each individual, in giving up the afflictions, is to be who he or she truly is. The end to be gained is freedom as a true individual.
In order for the end to be gained, even if only for one moment, the conditions have to be right, and the practice has to be sustained, over a certain period of time, in accordance with a true means-whereby principle, and in such a way that constant account is taken of the practitioner's individual strengths and weaknesses.
In general it may be true to say that, for the great majority of human beings, our strength is intelligence and our weakness is balance.
But this verse is ushering in a long series of verses in which faults and their antidotes are considered on a case by case basis. In that context, the word aatman in the third line seems to be important. Buddha/Ashvaghosha seems to be highlighting the existence of individual strengths and weaknesses -- between which the dividing line may be thin, as between humility and frailty, or as between confidence and pride, or as between persistence and fixity. Sensitivity, again, can be both a strength and a weakness, depending on individual circumstances.
Setting aside generalities, then, this verse as I read it is pointing the way to constructive conscious control of the individual.
kaalau = locative of kaala: time
vidhivat: according to rule, duly
pariikShya = absolutive of pariikSh: to look round , inspect carefully , try , examine , find out , observe , perceive
yogasya = genitive of yoga: formal practice
maatraam (accusative): f. measure (of any kind) , quantity , size , duration , number , degree
abhyupaayam (accusative): a means, an expedient
abale = locative of abala: want of strength, weakness
aatmani = locative of aatman: self, one's own
sampradhaarya = absolutive of sam-pra-√ dhR: to ponder , reflect , consider , deliberate or think about (acc.)
kaaryaH = nom. sg. m. kaarya (gerundiive of √kR): to be made or done or practised or performed
prayatnaH (nom. sg.): m. persevering effort , continued exertion or endeavour
tad: that, those [strength and weakness]
viruddhaH (nom. sg. m.): opposed; contrary, inconsistent or incompatible with
Examining duly the conditions of time and place as well as the scope and method of Yoga, a man should strive his utmost while having regard to the strong and weak points of his self and not doing what is contrary thereto.
Having considered the time and place for yogic practice, as prescribed, and also its extent and method, and after reflecting on your own strengths and weaknesses, make an effort, avoiding anything which conflicts with them.