I think all relationships require occasional maintenance effort, but the degree may vary over relationships and over time within the same relationship. As for the "not worth continuing" comment, I would assert that if a relationship either gets no maintenance work or is in constant maintenance mode, that's the time to start reassessing whether it's worth continuing. No work can mean stagnation and complacency, but too much work can mean that the relationship just isn't viable in the long-term.

I think relationship "work" can be enjoyable and can be chosen, but may not be either of those from time to time, and that the degree to which it usually is freely-chosen and enjoyable may well be indicative of how well the relationship will weather the times when it is miserable and forced upon you.