This weakness is worse than it first appears, and definitely the worst of the 4 new EOtE weaknesses.
It prevents you from taking more than one action of either "fight" or "activate" each turn. That doesn't seem so bad... until you realize that A LOT of things are "activate".
In fact, any action, printed on any card, with a , is an "activate" action, on top of its descriptor, if any. This includes, for example :
-most "resign" on locations or agendas / acts
-most weapons
-most clueing tools (fingerprint kit, lockpicks...)
-most spell assets (for fighting, clueing, evading...)
-some investigator specific abilities, like Preston Fairmont cashing in his inheritance and Lily Chen's Disciplines
-most "parlay" on enemies or bystanders
-a lot of special actions on locations that are mandatory to advance a scenario
This card car thoroughly mess with your planning, especially in low player counts / solo when you realize that you can't grab the last 2 clues with your spell then resign because they're both "activate"... The fact that weaknesses are added to a deck after it is completed only makes it worse : some decks can heal damage easily, while others will have no healing whatsoever.