I have two 10-year cats yet have rescused a 2-3 week old abandoned kitten (her mom has been a street cat near the English academy for 2 years at least, limps, has a crooked tail and has trouble eating (jaw injury?); she abandoned one kitten and carries around the other (the seafood restauranteur across the street buys expensive wet cat food for her).
I took the kitten to the vet, it got its shots for a viral infection of the eyes (two shots, dunno the 2nd), and like a baby i have to feed it every couple of hours, first with a syringe, then a mini-baby bottle. It opened its eyes, is active, needs constant bodily contact.
You can't save all, but you can save some. At least one.
My two angora cats are PISSED but, after 10 years of pampering, their meows behind a few hours of bedroom confinement falls on deaf ears.
I still feed an orange 6-month old male street cat who let's me sit next to him but not touch him, and i feed a black & white very friendly leg-rubbing cat who either has been abandoned or simply is usually let outside, though how ravenous she was in February makes me suspect the former. She has had two kittens, which she has broughr by the house thrice, though one cowers away and the other hisses despite i petting the mom and feeding them wet and dry food.
Life is always worth it.
Make a difference, of some sorts, hopefully helpful.