The problem is, though, that it often doesn't work that way, with everybody taking sometimes and giving sometimes, so that it all balances out in the end.
Lots of people are life's takers, and will be constantly 'looking out for number one'. They would never give, offer or help anybody else with anything, just out of friendship or kindness.
They're often the ones who will 'just ask for a little favour' when they want something, but will expect full recompense (maybe even with a decent element of profit) for every little thing that others ask them to do, and will denounce them as rude, unreasonable and disgraceful if they don't.
I'm thinking of the countless CF threads on here, where somebody will (e.g.) enjoy totally free accommodation, meals and travel for a month's holiday as a 'favour from a friend', but when the friend notices they're low on milk and asks the guest to grab some when they're out one day, the guest will hand it over and immediately ask for their £2 back.
Of course, none of us on here know how much OP's friend gives and takes in many other ways - or possibly doesn't.