all is grist that comes to the mill

all is grist that comes to the mill and all grist to the mill (something which brings profit or advantage to a person) — доброму вору все впору; всякое лыко в строку; все пригодится, ничем не побрезгует

Example: For a writer, human problems are all grist to the mill.

also
[all is fish that comes to his net]
[всякое лыко в строку]