A big rock can be completed like a task but you are correct that a big rock can require multiple tasks.
There are two areas on a task or big rock: the text area you can click to mark it as completed and the rest represents the area you can use to drag and drop.
Ah, I figured out the problem. Say your big rock is "Cook supper". If you place your cursor over "Cook Supper" and drag it to Monday, "Cook supper" (Big Rock) will be striked through. However if you place your cursor next to "Cook supper", and drag it to a certain day, it won't be striked through. This is confusing. Personally, I'm not sure why you'd strike through a Big Rock/Goal anyway. Strike through signifies completion - most Big Rocks/Goals will require many action steps until they're done. Perhaps you can use another visual sign to indicate that a Big Rock has been delegated to a certain day.
A big rock can be completed like a task but you are correct that a big rock can require multiple tasks.
There are two areas on a task or big rock: the text area you can click to mark it as completed and the rest represents the area you can use to drag and drop.