The phrase that helps remind me of not giving in to weariness (and we all get tired) is: Keeping on Keeping On.
Again this is not praying the same prayer in order to wear God down, it is being consistent, constant, and unwavering even when we don’t feel like it. I’m sure the widow wanted to give up and quit but she didn’t. Her life literally would have depended on her persistence. Do we consider our own steadfastness in prayer to be matter of life or death? Jesus surely does.