A hard thing to accept is that WE are to blame as well. Not just them.
We allowed ourselves to make up for what they didn't do and continued this behavior until it became accustomed.

They lack that responsibility because we habitually did it all ourselves, when we should have brought it up and had them take half the responsibility like they should.

It's similar to raising a child. Praise for every little thing they do begin to take part in, and discipline for their irresponsibility. The discipline is refusing to make up for their short comings and allow the consequence for their lack of planning and decision making to be put upon them.

"I asked you to decide on a date for this party. Have you decided?" "No." "Well, you need to tell our son that you have not thought about the date yet, and that his party will now be held back."

"Did you finance the money to buy a new washer like I asked?" No "Well, now we don't have a washer to wash the clothes. You will need to take them to the laundry mat."

If he doesn't, force yourself to allow the clothes to pile and pile until he finally does.

These are very vague examples but it's showing you what I mean by consequence being a discipline when they don't do what has become expected of them.