Mission creep is what group dynamics folks describe what the rest of us call L.O.S.T, or Line Of Sight Tasking (I'm still not sure what we call group dynamics without making our moms cry). At some point in a project one of the very bright people who came up with the original idea realizes there's yet another function s/he forgot within the transaction and announces 'someone needs to do/be .....' The first person who makes eye contact inherits this new responsibility with absolutely no authority or means to accomplish it. Don't look up! Oops, thanks for playing.
It's part of our lives as individuals, as well, fretting in the various roles we each play in the drama. I had a plateful (and more) when it was just me, myself and I. Falling in love and getting married moved me, or us, to egoisme a deux and then we added children to the mix. Solo, spouse, parent, while also being a child, sibling and wearing a half-dozen other hats. You can't tell the players without a scorecard, especially when we each are covering numerous positions.
Is there a limit to all this multi-tasking, if that's what this actually is (I like to think that term is better applied to linked tasks vice totally different ones such as a product being both a floor polish and a dessert topping) and when do we reach a limit, how do we know? I remember the 'how to cook a frog in boiling water' semi-urban legend (don't judge; I run with a colorful crowd, sehr bunte leute) that makes me suspect there's no 'top end.'
If you place a frog in a pot of boiling water, it will simply hop back out; but, if you place the frog in the pot of water and then slowly and carefully raise the heat of the flame under the pot, the frog will never move until it has been cooked. Look at who we are, from what we were and guess what we might become. I think we might be better off jumping.