sunk costs
This was hard because I struggle with sunk costs. In principle I know that once you've spent money or time or effort on something it's gone and you can't get it back -- so if it's not paying dividends, hanging on "to preserve your investment" does not help. There's no such thing. If it's a faulty product and you can possibly get some of your money back that's one thing, but otherwise, sunk costs are gone and should not affect current decisions. This idea usually applies to investments (if the stock is tanking and you don't think it'll change, get rid of it), but sunk costs aren't just about money.
Yeah, intellectually I know all that, but it was still hard to close that browser tab. I want the time I spent on that site to matter; I want to feel good about what we built. It was hard to start to walk away from the SCA years ago too -- same principle, though measured in years rather than months. (I'm still minimally active, but I choose carefully what I want to do.) And historically I have had a great deal of trouble leaving jobs that are no longer fulfilling because I've invested in them. In all of these cases the answer is to be happy for the good times and recognize that things change and that can mean that things you invested in are no longer worth sticking around for. My intellect knows this; could it please arrange to convince my heart of it too?

no subject
I have similar issues with sunk costs of my time and caring. It's hard, and sometimes you just have to just grit your teeth and let go of something even though you still have ties to it. That part is easier said than done!